LibVideo: Remove Starting playback state in favor of Seeking to zero

Author: https://github.com/Zaggy1024
Commit: e391f18e9e
Pull-request: https://github.com/SerenityOS/serenity/pull/18300
Reviewed-by: https://github.com/AtkinsSJ ✅
Reviewed-by: https://github.com/trflynn89

Userland/Libraries/LibVideo/PlaybackManager.h

@@ -92,7 +92,6 @@ public:
 };
 
 enum class PlaybackState {
-    Starting,
     Playing,
     Paused,
     Buffering,
@@ -146,7 +145,6 @@ private:
     class PlaybackStateHandler;
     // Abstract class to allow resuming play/pause after the state is completed.
     class ResumingStateHandler;
-    class StartingStateHandler;
     class PlayingStateHandler;
     class PausedStateHandler;
     class BufferingStateHandler;