More cleanups of custom classes in favor of .NET runtime types.

Source/Game/Globals/ObjectManager.cs

@@ -19,7 +19,6 @@ using Framework.Collections;
 using Framework.Constants;
 using Framework.Database;
 using Framework.Dynamic;
-using Framework.GameMath;
 using Framework.IO;
 using Game.Conditions;
 using Game.DataStorage;
@@ -32,6 +31,7 @@ using Game.Spells;
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Numerics;
 using System.Runtime.InteropServices;
 
 namespace Game
@@ -4257,10 +4257,10 @@ namespace Game
                     gameObjectAddon.invisibilityValue = 1;
                 }
 
-                if (!gameObjectAddon.ParentRotation.isUnit())
+                if (!(Math.Abs(Quaternion.Dot(gameObjectAddon.ParentRotation, gameObjectAddon.ParentRotation) - 1) < 1e-5))
                 {
                     Log.outError(LogFilter.Sql, $"GameObject (GUID: {guid}) has invalid parent rotation in `gameobject_addon`, set to default");
-                    gameObjectAddon.ParentRotation = Quaternion.WAxis;
+                    gameObjectAddon.ParentRotation = Quaternion.Identity;
                 }
 
                 if (gameObjectAddon.WorldEffectID != 0 && !CliDB.WorldEffectStorage.ContainsKey(gameObjectAddon.WorldEffectID))