Fix beatmap panels locally handling mod changes unnecessarily

The `BeatmapDifficultyCache` handles mod changes, so handling locally is
unnecessary. By handling locally, it creates a visual issue when
adjusting mods often. Test using Ctrl +/- at song select and observing
that without this change, the star rating will flicker back to the
default due to the local re-fetch.

osu.Game/Screens/SelectV2/PanelBeatmap.cs

@@ -205,11 +205,7 @@ namespace osu.Game.Screens.SelectV2
                 updateKeyCount();
             });
 
-            mods.BindValueChanged(_ =>
-            {
-                computeStarRating();
-                updateKeyCount();
-            }, true);
+            mods.BindValueChanged(_ => updateKeyCount(), true);
         }
 
         protected override void PrepareForUse()