pkg/useragent: remove // import comments

These comments were added to enforce using the correct import path for
our packages ("github.com/docker/docker", not "github.com/moby/moby").
However, when working in go module mode (not GOPATH / vendor), they have
no effect, so their impact is limited.

Remove these imports in preparation of migrating our code to become an
actual go module.

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

pkg/useragent/useragent.go

@@ -1,6 +1,6 @@
 // Package useragent provides helper functions to pack
 // version information into a single User-Agent header.
-package useragent // import "github.com/docker/docker/pkg/useragent"
+package useragent
 
 import (
 	"strings"

pkg/useragent/useragent_test.go

@@ -1,4 +1,4 @@
-package useragent // import "github.com/docker/docker/pkg/useragent"
+package useragent
 
 import "testing"