fix: Prepares for IPooledEnumerable removal (#1548)

### Summary

- Removes `IPooledEnumerable` (non-generic)
- Changes `IPooledEnumerable<T>` so that  `Free()` is replaced with the `IDisposable` pattern

Projects/UOContent/Spells/Sixth/MassCurse.cs

@@ -54,8 +54,6 @@ namespace Server.Spells.Sixth
 
                         HarmfulSpell(m);
                     }
-
-                    eable.Free();
                 }
             }
 

Projects/UOContent/Spells/Sixth/Reveal.cs

@@ -53,8 +53,6 @@ namespace Server.Spells.Sixth
                         m.FixedParticles(0x375A, 9, 20, 5049, EffectLayer.Head);
                         m.PlaySound(0x1FD);
                     }
-
-                    eable.Free();
                 }
             }