Revert "GStreamerSharp: Fix playbin flags"

This reverts commit bfa80beb46a7fc1850b22955c6eaff1b4751a0fd
because it breaks video playback and causes these warnings:

[1 Warn  18:18:14.483] Error running PlayerEngine handler for StateChange - System.NullReferenceException: Object reference not set to an instance of an object (in `Banshee.ThickClient')
  at Banshee.Gui.PlaybackActions.OnPlayerStateChange (Banshee.MediaEngine.PlayerEventStateChangeArgs args) [0x00067] in /home/knocte/Documents/Code/bansheeGSTS1/src/Core/Banshee.ThickClient/Banshee.Gui/PlaybackActions.cs:155
  at Banshee.Gui.PlaybackActions.OnPlayerEvent (Banshee.MediaEngine.PlayerEventArgs args) [0x0006b] in /home/knocte/Documents/Code/bansheeGSTS1/src/Core/Banshee.ThickClient/Banshee.Gui/PlaybackActions.cs:141
  at Banshee.MediaEngine.PlayerEngineService.RaiseEvent (Banshee.MediaEngine.PlayerEventArgs args) [0x0007c] in /home/knocte/Documents/Code/bansheeGSTS1/src/Core/Banshee.Services/Banshee.MediaEngine/PlayerEngineService.cs:922
[1 Debug 18:18:14.485] Player state change: Loaded -> Playing
[1 Debug 18:18:14.608] Querying model for track to play in song:Next mode
[1 Warn  18:18:14.621] Failed to pre-buffer next track - System.InvalidCastException: Cannot cast from source type to destination type. (in `Banshee.GStreamerSharp')
  at Banshee.GStreamerSharp.PlayerEngine.LookupForSubtitle (Hyena.SafeUri uri) [0x0000c] in /home/knocte/Documents/Code/bansheeGSTS1/src/Backends/Banshee.GStreamerSharp/Banshee.GStreamerSharp/PlayerEngine.cs:718
  at Banshee.GStreamerSharp.PlayerEngine.SetNextTrackUri (Hyena.SafeUri uri, Boolean maybeVideo) [0x00050] in /home/knocte/Documents/Code/bansheeGSTS1/src/Backends/Banshee.GStreamerSharp/Banshee.GStreamerSharp/PlayerEngine.cs:468
  at Banshee.MediaEngine.PlayerEngine.HandleNextTrack (Banshee.Collection.TrackInfo track) [0x0006c] in /home/knocte/Documents/Code/bansheeGSTS1/src/Core/Banshee.Services/Banshee.MediaEngine/PlayerEngine.cs:123