make ModDifficultyAdjust generic

osu.Game.Rulesets.Mania/Mods/ManiaModDifficultyAdjust.cs

@@ -1,22 +0,0 @@
-// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
-// See the LICENCE file in the repository root for full licence text.
-
-using osu.Framework.Bindables;
-using osu.Game.Configuration;
-using osu.Game.Rulesets.Mods;
-
-namespace osu.Game.Rulesets.Mania.Mods
-{
-    public class ManiaModDifficultyAdjust : ModDifficultyAdjust
-    {
-        [SettingSource("Overall Difficulty", "Override the beatmap's set OD")]
-        public override BindableNumber<float> OverallDifficulty { get; } = new BindableFloat
-        {
-            MinValue = 1,
-            MaxValue = 10,
-            Default = 5,
-            Value = 5,
-            Precision = 0.1F,
-        };
-    }
-}