fix event loop timing issue

The event loop tries to run no faster than every 10ms. If it detects
that it goes faster, it would incorrectly calculate the difference, and
then wait (what I assume was) way too long or too short.
Either way, now it's fixed and it correctly works, even when introducing
new lua states.

include/TPluginMonitor.h

@@ -18,6 +18,5 @@ public:
 private:
     std::shared_ptr<TLuaEngine> mEngine;
     fs::path mPath;
-    std::atomic_bool mShutdown { false };
     std::unordered_map<std::string, fs::file_time_type> mFileTimes;
 };