Scripts/Northrend: Knockbackimmunity Cleanup

(cherry picked from commit c560cb0a0c)

src/server/scripts/World/npcs_special.cpp

@@ -1488,7 +1488,6 @@ public:
         {
             // TODO: solve this in a different way! setting them as stunned prevents dummies from parrying
             me->SetControlled(true, UNIT_STATE_STUNNED);//disable rotate
-            me->ApplySpellImmune(0, IMMUNITY_EFFECT, SPELL_EFFECT_KNOCK_BACK, true);//imune to knock aways like blast wave
 
             _events.Reset();
             _damageTimes.clear();