use format string when using printf like commands

As per https://github.com/golang/go/issues/60529, printf like commands with
non-constant format strings and no args give an error in govet

Signed-off-by: Akhil Mohan <akhilerm@gmail.com>

plugins/services/content/contentserver/contentserver.go

@@ -133,7 +133,7 @@ func (s *service) Delete(ctx context.Context, req *api.DeleteContentRequest) (*p
 	log.G(ctx).WithField("digest", req.Digest).Debugf("delete content")
 	dg, err := digest.Parse(req.Digest)
 	if err != nil {
-		return nil, status.Errorf(codes.InvalidArgument, err.Error())
+		return nil, status.Error(codes.InvalidArgument, err.Error())
 	}
 
 	if err := s.store.Delete(ctx, dg); err != nil {