C# 9 Cleanup (#325)

- [X] Removes EventArgs - not needed
- [X] Merges sequential checks
- [X] Removes redundant type declarations

Projects/UOContent/Spells/Ninjitsu/Backstab.cs

@@ -9,7 +9,7 @@ namespace Server.Spells.Ninjitsu
         public override double RequiredSkill => Core.ML ? 40.0 : 20.0;
 
         public override TextDefinition AbilityMessage =>
-            new TextDefinition(1063089); // You prepare to Backstab your opponent.
+            new(1063089); // You prepare to Backstab your opponent.
 
         public override bool ValidatesDuringHit => false;