core: settings: Untangle multicore from asynchronous GPU.

- Now that GPU is always threaded, we can support multicore with synchronous GPU.

src/core/settings.h

@@ -257,7 +257,4 @@ void LogSettings();
 // Restore the global state of all applicable settings in the Values struct
 void RestoreGlobalState(bool is_powered_on);
 
-// Fixes settings that are known to cause issues with the emulator
-void Sanitize();
-
 } // namespace Settings