Remove unused previewTrackManager variable
Remove unused previewTrackManager variable

DrabWeb/osu,NeoAdonis/osu,ZLima12/osu,smoogipoo/osu,peppy/osu,naoey/osu,ppy/osu,DrabWeb/osu,smoogipooo/osu,smoogipoo/osu,ZLima12/osu,2yangk23/osu,UselessToucan/osu,DrabWeb/osu,UselessToucan/osu,2yangk23/osu,UselessToucan/osu,EVAST9919/osu,ppy/osu,peppy/osu,peppy/osu,naoey/osu,smoogipoo/osu,EVAST9919/osu,johnneijzen/osu,peppy/osu-new,naoey/osu,NeoAdonis/osu,NeoAdonis/osu,johnneijzen/osu,ppy/osu