Core/Spell: fix target checks

- Aura will be applied at last moment possible (after damage) to prevent regressions on #18395
- Partial revert of 9b38a6352c0fe2499de54fd769aa1c721a410bda as it wasnt handling correctly checks without spells

src/server/game/Spells/SpellEffects.cpp

@@ -953,10 +953,6 @@ void Spell::EffectApplyAura(SpellEffIndex effIndex)
         aurApp = unitTarget->_CreateAuraApplication(_spellAura, 1 << effIndex);
     else
         aurApp->UpdateApplyEffectMask(aurApp->GetEffectsToApply() | 1 << effIndex);
-
-    // apply effect on target (skip for reapply)
-    if (!aurApp->HasEffect(effIndex))
-        unitTarget->_ApplyAuraEffect(_spellAura, effIndex);
 }
 
 void Spell::EffectUnlearnSpecialization(SpellEffIndex effIndex)