Merge pull request #30619 from Givikap120/remove_unnecessary_field

Remove field that's used only in one method

osu.Game.Rulesets.Osu/Difficulty/Skills/OsuStrainSkill.cs

@@ -23,16 +23,14 @@ public abstract class OsuStrainSkill : StrainSkill
         /// </summary>
         protected virtual double ReducedStrainBaseline => 0.75;
 
-        protected double Difficulty;
-
         protected OsuStrainSkill(Mod[] mods)
             : base(mods)
         {
         }
 
         public override double DifficultyValue()
         {
-            Difficulty = 0;
+            double difficulty = 0;
             double weight = 1;
 
             // Sections with 0 strain are excluded to avoid worst-case time complexity of the following sort (e.g. /b/2351871).
@@ -52,11 +50,11 @@ public override double DifficultyValue()
             // We're sorting from highest to lowest strain.
             foreach (double strain in strains.OrderDescending())
             {
-                Difficulty += strain * weight;
+                difficulty += strain * weight;
                 weight *= DecayWeight;
             }
 
-            return Difficulty;
+            return difficulty;
         }
 
         public static double DifficultyToPerformance(double difficulty) => Math.Pow(5.0 * Math.Max(1.0, difficulty / 0.0675) - 4.0, 3.0) / 100000.0;