Make missing beatmap notification simple

Progress didn't work for several reasons:

- It was spinning when nothing was actually happening yet
  (especially egregious with autodownload off)

- It was blocking exits (as all progress notifications do)

- When actually going to download, two progress notifications would
  pertain to one thing

- It wasn't helping much with the actual implementation of score
  re-import, cancelling the progress notification would result in
  similarly jank UX of beatmap importing but not the score.

osu.Game/Database/MissingBeatmapNotification.cs

@@ -18,7 +18,7 @@ using osu.Game.Localisation;
 
 namespace osu.Game.Database
 {
-    public partial class MissingBeatmapNotification : ProgressNotification
+    public partial class MissingBeatmapNotification : SimpleNotification
     {
         [Resolved]
         private BeatmapModelDownloader beatmapDownloader { get; set; } = null!;
@@ -93,7 +93,7 @@ namespace osu.Game.Database
             if (sender.Any(s => s.Beatmaps.Any(b => b.MD5Hash == beatmapHash)))
             {
                 var importTask = new ImportTask(scoreStream, "score.osr");
-                scoreManager.Import(this, new[] { importTask });
+                scoreManager.Import(new[] { importTask });
                 realmSubscription?.Dispose();
             }
         }