Fix `TestScenePlaylistsScreen` crashing on entering room

osu.Game.Tests/Visual/Playlists/TestScenePlaylistsScreen.cs

@@ -2,8 +2,6 @@
 // See the LICENCE file in the repository root for full licence text.
 
 using NUnit.Framework;
-using osu.Framework.Allocation;
-using osu.Game.Overlays;
 
 namespace osu.Game.Tests.Visual.Playlists
 {
@@ -12,9 +10,6 @@ public class TestScenePlaylistsScreen : ScreenTestScene
     {
         protected override bool UseOnlineAPI => true;
 
-        [Cached]
-        private MusicController musicController { get; set; } = new MusicController();
-
         public TestScenePlaylistsScreen()
         {
             var multi = new Screens.OnlinePlay.Playlists.Playlists();