Drop experimental tag for manifest commands

Some of us working on Kubernetes have been using the docker manifest
experimental commands to build images for some time now. The last
problem we had was fixed by one of the commits a few months ago:
69e1743

Could we please promote these commands from experimental to GA

Change-Id: Iaa3ac7e1b56e1b6b4f091d047bf50c6794fa3d65

Author: dims

cli/command/manifest/cmd.go

@@ -20,7 +20,6 @@ func NewManifestCommand(dockerCli command.Cli) *cobra.Command {
 		Run: func(cmd *cobra.Command, args []string) {
 			fmt.Fprintf(dockerCli.Err(), "\n"+cmd.UsageString())
 		},
-		Annotations: map[string]string{"experimentalCLI": ""},
 	}
 	cmd.AddCommand(
 		newCreateListCommand(dockerCli),