Fix compile failures

Author: bdach

Templates/Rulesets/ruleset-empty/osu.Game.Rulesets.EmptyFreeform/EmptyFreeformDifficultyCalculator.cs

@@ -21,7 +21,7 @@ public EmptyFreeformDifficultyCalculator(IRulesetInfo ruleset, IWorkingBeatmap b
 
         protected override IDifficultyAttributes CreateDifficultyAttributes(IBeatmap beatmap, Mod[] mods, Skill[] skills, double clockRate)
         {
-            return new EmptyDifficultyAttributes();
+            return new DifficultyAttributes();
         }
 
         protected override IEnumerable<DifficultyHitObject> CreateDifficultyHitObjects(IBeatmap beatmap, double clockRate) => Enumerable.Empty<DifficultyHitObject>();

Templates/Rulesets/ruleset-example/osu.Game.Rulesets.Pippidon/PippidonDifficultyCalculator.cs

@@ -21,7 +21,7 @@ public PippidonDifficultyCalculator(IRulesetInfo ruleset, IWorkingBeatmap beatma
 
         protected override IDifficultyAttributes CreateDifficultyAttributes(IBeatmap beatmap, Mod[] mods, Skill[] skills, double clockRate)
         {
-            return new EmptyDifficultyAttributes();
+            return new DifficultyAttributes();
         }
 
         protected override IEnumerable<DifficultyHitObject> CreateDifficultyHitObjects(IBeatmap beatmap, double clockRate) => Enumerable.Empty<DifficultyHitObject>();

Templates/Rulesets/ruleset-scrolling-empty/osu.Game.Rulesets.EmptyScrolling/EmptyScrollingDifficultyCalculator.cs

@@ -21,7 +21,7 @@ public EmptyScrollingDifficultyCalculator(IRulesetInfo ruleset, IWorkingBeatmap
 
         protected override IDifficultyAttributes CreateDifficultyAttributes(IBeatmap beatmap, Mod[] mods, Skill[] skills, double clockRate)
         {
-            return new EmptyDifficultyAttributes();
+            return new DifficultyAttributes();
         }
 
         protected override IEnumerable<DifficultyHitObject> CreateDifficultyHitObjects(IBeatmap beatmap, double clockRate) => Enumerable.Empty<DifficultyHitObject>();

Templates/Rulesets/ruleset-scrolling-example/osu.Game.Rulesets.Pippidon/PippidonDifficultyCalculator.cs

@@ -21,7 +21,7 @@ public PippidonDifficultyCalculator(IRulesetInfo ruleset, IWorkingBeatmap beatma
 
         protected override IDifficultyAttributes CreateDifficultyAttributes(IBeatmap beatmap, Mod[] mods, Skill[] skills, double clockRate)
         {
-            return new EmptyDifficultyAttributes();
+            return new DifficultyAttributes();
         }
 
         protected override IEnumerable<DifficultyHitObject> CreateDifficultyHitObjects(IBeatmap beatmap, double clockRate) => Enumerable.Empty<DifficultyHitObject>();