Don't call GameHost.Collect() twice

We already trim memory on a `SDL_EVENT_LOW_MEMORY`.

osu.Framework.Android/AndroidGameActivity.cs

@@ -80,12 +80,6 @@ namespace osu.Framework.Android
             }
         }
 
-        public override void OnTrimMemory(TrimMemory level)
-        {
-            base.OnTrimMemory(level);
-            host?.Collect();
-        }
-
         protected override void OnStop()
         {
             base.OnStop();