Move event handling logic to a dedicated class

Now all pieces are in place to allow handling events over multiple
socket connections.

src/wine-host/bridges/vst2.h

@@ -29,9 +29,9 @@
 #include <boost/asio/local/stream_protocol.hpp>
 #include <mutex>
 
+#include "../../common/communication.h"
 #include "../../common/configuration.h"
 #include "../../common/logging.h"
-#include "../../common/communication.h"
 #include "../editor.h"
 #include "../utils.h"
 
@@ -210,13 +210,6 @@ class Vst2Bridge {
      */
     Win32Thread process_replacing_handler;
 
-    /**
-     * A binary semaphore to prevent race conditions from the host callback
-     * function being called by two threads at once. See `send_event()` for more
-     * information.
-     */
-    std::mutex host_callback_mutex;
-
     /**
      * A scratch buffer for sending and receiving data during `process` and
      * `processReplacing` calls.