always hornor client side to choose which builder to use with DOCKER_BUILDKIT env var regardless the server setup

Signed-off-by: Anda Xu <anda.xu@docker.com>
(cherry picked from commit 5d931705e33927ba9f0b7251b74b6b3c450edaf6)
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

api/server/router/build/build_routes.go

@@ -250,12 +250,6 @@ func (br *buildRouter) postBuild(ctx context.Context, w http.ResponseWriter, r *
 		return errdefs.InvalidParameter(errors.New("squash is only supported with experimental mode"))
 	}
 
-	builderVersion := BuilderVersion(*br.features)
-	// check if the builder feature has been enabled from daemon as well.
-	if buildOptions.Version == types.BuilderBuildKit && builderVersion != "" && builderVersion != types.BuilderBuildKit {
-		return errdefs.InvalidParameter(errors.New("buildkit is not enabled on daemon"))
-	}
-
 	out := io.Writer(output)
 	if buildOptions.SuppressOutput {
 		out = notVerboseBuffer