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/component-handler-proxy.cpp

@@ -61,7 +61,7 @@ Vst3ComponentHandlerProxyImpl::endEdit(Steinberg::Vst::ParamID id) {
 
 tresult PLUGIN_API
 Vst3ComponentHandlerProxyImpl::restartComponent(int32 flags) {
-    return bridge.send_mutually_recursive_message<false>(
+    return bridge.send_mutually_recursive_message(
         YaComponentHandler::RestartComponent{
             .owner_instance_id = owner_instance_id(), .flags = flags});
 }