Remove signature store from registry. Return a generated signature for manifest

pull.

Signed-off-by: Richard Scothern <richard.scothern@docker.com>

registry/root.go

@@ -69,7 +69,7 @@ var GCCmd = &cobra.Command{
 			os.Exit(1)
 		}
 
-		registry, err := storage.NewRegistry(ctx, driver, storage.DisableSchema1Signatures, storage.Schema1SigningKey(k))
+		registry, err := storage.NewRegistry(ctx, driver, storage.Schema1SigningKey(k))
 		if err != nil {
 			fmt.Fprintf(os.Stderr, "failed to construct registry: %v", err)
 			os.Exit(1)