Make `OsuGame.ScreenChanged` `private` and non-`virtual`
Make `OsuGame.ScreenChanged` `private` and non-`virtual`

Just reducing complexity scope here.

peppy/osu,NeoAdonis/osu,peppy/osu,ppy/osu,peppy/osu,ppy/osu,NeoAdonis/osu,ppy/osu,NeoAdonis/osu