disable debugging groups in non-debug builds

Use a macro to completely remove all instantiations of mbgl::gl::debugging::group so that we aren't executing the code to generate the arguments to the object instantiation

src/mbgl/map/source.cpp

@@ -186,7 +186,7 @@ void Source::updateMatrices(const mat4 &projMatrix, const TransformState &transf
 void Source::drawClippingMasks(Painter &painter) {
     for (const auto& pair : tiles) {
         Tile &tile = *pair.second;
-        gl::debugging::group group(std::string { "mask: " } + std::string(tile.id));
+        MBGL_DEBUG_GROUP(std::string { "mask: " } + std::string(tile.id));
         painter.drawClippingMask(tile.matrix, tile.clip);
     }
 }