Fix a bunch of compiler warnings (#10518)

Content.Client/Audio/BackgroundAudioSystem.cs

@@ -24,7 +24,6 @@ namespace Content.Client.Audio
         [Dependency] private readonly IBaseClient _client = default!;
         [Dependency] private readonly IConfigurationManager _configManager = default!;
         [Dependency] private readonly IGameTiming _timing = default!;
-        [Dependency] private readonly IMapManager _mapManager = default!;
         [Dependency] private readonly IPlayerManager _playMan = default!;
         [Dependency] private readonly IPrototypeManager _prototypeManager = default!;
         [Dependency] private readonly IRobustRandom _robustRandom = default!;