Revert "Separate mutual recursion on GUI and other threads"

This reverts commit a495f1a67f.

This ended up not being an issue. What we _do_ have to do, sadly, is to
have a mutual recursion context stack per plugin. Otherwise multiple
plugin instances can deadlock eachother.

src/wine-host/bridges/vst3-impls/plug-frame-proxy.cpp

@@ -46,9 +46,8 @@ Vst3PlugFrameProxyImpl::resizeView(Steinberg::IPlugView* /*view*/,
         // We have to use this special sending function here so we can handle
         // calls to `IPlugView::onSize()` from this same thread (the UI thread).
         // See the docstring for more information.
-        return bridge.send_mutually_recursive_message<true>(
-            YaPlugFrame::ResizeView{.owner_instance_id = owner_instance_id(),
-                                    .new_size = *newSize});
+        return bridge.send_mutually_recursive_message(YaPlugFrame::ResizeView{
+            .owner_instance_id = owner_instance_id(), .new_size = *newSize});
     } else {
         std::cerr
             << "WARNING: Null pointer passed to 'IPlugFrame::resizeView()'"