Make realm a non-drawable component to better order disposal

Until now, the `RealmContextFactory` would be disposed as part of the
drawable hierarchy. This is too early, as it may be being used by higher
level components (like `ConfigManager`s, see #15115) that perform final
operations after the drawables have been disposed.

Seems to make sense moving this out of the drawable hierarchy and in
line with how we were doing things with EF.

osu.Game/OsuGameBase.cs

@@ -187,8 +187,6 @@ namespace osu.Game
 
             dependencies.Cache(realmFactory = new RealmContextFactory(Storage, "client"));
 
-            AddInternal(realmFactory);
-
             dependencies.CacheAs(Storage);
 
             var largeStore = new LargeTextureStore(Host.CreateTextureLoaderStore(new NamespacedResourceStore<byte[]>(Resources, @"Textures")));
@@ -529,6 +527,7 @@ namespace osu.Game
             LocalConfig?.Dispose();
 
             contextFactory?.FlushConnections();
+            realmFactory?.Dispose();
         }
     }
 }