Remove separate menu FPS throttling

We should let VSync/m_max_fps (which defaults to 120) do their job.  If a monitor has a refresh rate even slightly higher than 60FPS (e.g. 60.0007FPS), throttling will introduce stutters, even more so at modern high refresh rates (75, 90, 120, etc.)

This also cleans up the code, e.g. the var name `m_throttle_fps` was also being used in the main loop for a different function, despite having the same var name.

src/main_loop.cpp

@@ -296,10 +296,8 @@ float MainLoop::getLimitedDt()
 #else
         const int max_fps = (irr_driver->isRecording() &&
                              UserConfigParams::m_limit_game_fps )
-                          ? UserConfigParams::m_record_fps 
-                          : ( StateManager::get()->throttleFPS() 
-                              ? 60 
-                              : UserConfigParams::m_max_fps     );
+                           ? UserConfigParams::m_record_fps 
+                           : UserConfigParams::m_max_fps;
 #endif
         const int current_fps = (int)(1000.0f / dt);
         if (!m_throttle_fps || current_fps <= max_fps ||