Remove all gogoproto extensions

This commit removes the following gogoproto extensions;

- gogoproto.nullable
- gogoproto.customename
- gogoproto.unmarshaller_all
- gogoproto.stringer_all
- gogoproto.sizer_all
- gogoproto.marshaler_all
- gogoproto.goproto_unregonized_all
- gogoproto.goproto_stringer_all
- gogoproto.goproto_getters_all

None of them are supported by Google's toolchain (see #6564).

Signed-off-by: Kazuyoshi Kato <katokazu@amazon.com>

cmd/ctr/commands/plugins/plugins.go

@@ -146,7 +146,7 @@ var listCommand = cli.Command{
 	},
 }
 
-func prettyPlatforms(pspb []types.Platform) string {
+func prettyPlatforms(pspb []*types.Platform) string {
 	psm := map[string]struct{}{}
 	for _, p := range pspb {
 		psm[platforms.Format(v1.Platform{