Fix build by removing non existent namespace

Looks like a wrong auto merge. (We really should fix CI)

MediaBrowser.Providers/Music/MusicBrainzAlbumProvider.cs

@@ -15,7 +15,6 @@ using MediaBrowser.Controller.Providers;
 using MediaBrowser.Model.Entities;
 using MediaBrowser.Model.Providers;
 using MediaBrowser.Model.Serialization;
-using MediaBrowser.Model.Xml;
 using Microsoft.Extensions.Configuration;
 using Microsoft.Extensions.Logging;