daemon/server/backend: align DiskUsage types with api

Make the "per-object" types aliases for the API type, and remove
the BuildCacheDiskUsage type, as it's not currently used.

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

daemon/server/backend/disk_usage.go

@@ -28,41 +28,14 @@ type DiskUsage struct {
 	Images     *ImageDiskUsage
 	Containers *ContainerDiskUsage
 	Volumes    *VolumeDiskUsage
-	BuildCache *BuildCacheDiskUsage
-}
-
-// BuildCacheDiskUsage contains disk usage for the build cache.
-type BuildCacheDiskUsage struct {
-	ActiveCount int64
-	TotalCount  int64
-	TotalSize   int64
-	Reclaimable int64
-	Items       []build.CacheRecord
+	BuildCache *build.DiskUsage
 }
 
 // ContainerDiskUsage contains disk usage for containers.
-type ContainerDiskUsage struct {
-	ActiveCount int64
-	TotalCount  int64
-	TotalSize   int64
-	Reclaimable int64
-	Items       []container.Summary
-}
+type ContainerDiskUsage = container.DiskUsage
 
 // ImageDiskUsage contains disk usage for images.
-type ImageDiskUsage struct {
-	ActiveCount int64
-	TotalCount  int64
-	TotalSize   int64
-	Reclaimable int64
-	Items       []image.Summary
-}
+type ImageDiskUsage = image.DiskUsage
 
 // VolumeDiskUsage contains disk usage for volumes.
-type VolumeDiskUsage struct {
-	ActiveCount int64
-	TotalCount  int64
-	TotalSize   int64
-	Reclaimable int64
-	Items       []volume.Volume
-}
+type VolumeDiskUsage = volume.DiskUsage