fix(Core/Misc): Revert commits causing massive delays (#10408)

* this reverts commit (https://github.com/azerothcore/azerothcore-wotlk/commit/674b168addbc35f1faaa2e72eacee6edf5e0d457)

* this reverts commit (https://github.com/azerothcore/azerothcore-wotlk/commit/b085ee61ebfcc85505bab405e15b059943425678)

* closes https://github.com/azerothcore/azerothcore-wotlk/issues/10407

src/server/game/Spells/SpellEffects.cpp

@@ -293,9 +293,6 @@ void Spell::EffectInstaKill(SpellEffIndex /*effIndex*/)
     data << unitTarget->GetGUID();
     data << uint32(m_spellInfo->Id);
     m_caster->SendMessageToSet(&data, true);
-    // MDic - acidmanifesto: This is needed due to the Unit::DealDamage firing off immediately after the worldpacket which nerfs out additional spell animations
-    // The delay of half a second ensures the spell animations which are typically 0.4 seconds long have enough time to fire off
-    std::this_thread::sleep_for(500ms);
 
     Unit::DealDamage(m_caster, unitTarget, unitTarget->GetHealth(), nullptr, NODAMAGE, SPELL_SCHOOL_MASK_NORMAL, nullptr, false);
 }