fix: Fixes double calls with Target cancel and spell sequences (#1840)

### Summary
- Cleans up target cancellation being called incorrectly.
- An invalid target type (which should never happen), now calls `OnTargetUntargetable` instead of `OnTargetCanceled`
- Removes double calls to `FinishSequence` in Spells.

Projects/UOContent/Spells/Seventh/ChainLightning.cs

@@ -95,8 +95,6 @@ namespace Server.Spells.Seventh
                     }
                 }
             }
-
-            FinishSequence();
         }
 
         public override void OnCast()

Projects/UOContent/Spells/Seventh/EnergyField.cs

@@ -67,8 +67,6 @@ public class EnergyFieldSpell : MagerySpell, ISpellTargetingPoint3D
                 );
             }
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()

Projects/UOContent/Spells/Seventh/FlameStrike.cs

@@ -54,8 +54,6 @@ namespace Server.Spells.Seventh
 
                 SpellHelper.Damage(this, m, damage, 0, 100, 0, 0, 0);
             }
-
-            FinishSequence();
         }
 
         public override void OnCast()

Projects/UOContent/Spells/Seventh/GateTravel.cs

@@ -94,8 +94,6 @@ public class GateTravelSpell : MagerySpell, IRecallSpell
             firstGate.LinkedGate = secondGate;
             secondGate.LinkedGate = firstGate;
         }
-
-        FinishSequence();
     }
 
     public override void OnCast()
@@ -107,6 +105,7 @@ public class GateTravelSpell : MagerySpell, IRecallSpell
         else
         {
             Effect(m_Entry.Location, m_Entry.Map, true);
+            FinishSequence();
         }
     }
 

Projects/UOContent/Spells/Seventh/ManaVampire.cs

@@ -75,8 +75,6 @@ namespace Server.Spells.Seventh
 
                 HarmfulSpell(m);
             }
-
-            FinishSequence();
         }
 
         public override void OnCast()

Projects/UOContent/Spells/Seventh/MassDispel.cs

@@ -72,8 +72,6 @@ namespace Server.Spells.Seventh
                     }
                 }
             }
-
-            FinishSequence();
         }
 
         public override void OnCast()

Projects/UOContent/Spells/Seventh/MeteorSwarm.cs

@@ -100,8 +100,6 @@ namespace Server.Spells.Seventh
                     }
                 }
             }
-
-            FinishSequence();
         }
 
         public override void OnCast()