api/docs: remove BuildCache.Parent field for API v1.42 and up

The BuildCache.Parent field was removed in API v1.42 in [moby@e0db820].
While we had to keep the Go struct field around to backfil the field for
older API versions, it's no longer part of API v1.42 and up (using the
"omitempty" is just an implementation detail).

This patch corrects the swagger files to match this.

[moby@e0db820]: e0db8207f3

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

api/docs/v1.42.yaml

@@ -2619,14 +2619,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.43.yaml

@@ -2650,14 +2650,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.44.yaml

@@ -2661,14 +2661,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.45.yaml

@@ -2647,14 +2647,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.46.yaml

@@ -2693,14 +2693,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.47.yaml

@@ -2711,14 +2711,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.48.yaml

@@ -2812,14 +2812,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.49.yaml

@@ -2812,14 +2812,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.50.yaml

@@ -2639,14 +2639,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.51.yaml

@@ -2653,14 +2653,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/docs/v1.52.yaml

@@ -2730,14 +2730,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.

api/swagger.yaml

@@ -2730,14 +2730,6 @@ definitions:
         description: |
           Unique ID of the build cache record.
         example: "ndlpt0hhvkqcdfkputsk4cq9c"
-      Parent:
-        description: |
-          ID of the parent build cache record.
-
-          > **Deprecated**: This field is deprecated, and omitted if empty.
-        type: "string"
-        x-nullable: true
-        example: ""
       Parents:
         description: |
           List of parent build cache record IDs.