Core/Spells: remove incorrect PvP combat state

by @P-Kito; retrieved from #15027

Neither Vampiric Embrace nor Wandering Plague
should keep PvP players in combat state.

Players can't drink for extended periods of time in arena
debuffed with Death Knight's Wandering Plague + diseases
or when the counterpart is buffed with Vampiric Embrace.
Every tick keeps them in combat. This PR should fix the issue.

src/server/game/Spells/SpellMgr.cpp

@@ -3235,6 +3235,9 @@ void SpellMgr::LoadSpellInfoCorrections()
                 spellInfo->Effects[EFFECT_1].BasePoints = -6; // -5%
                 break;
             case 50526: // Wandering Plague
+            case 15290: // Vampiric Embrace
+                spellInfo->AttributesEx3 |= SPELL_ATTR3_NO_INITIAL_AGGRO;
+                break;
             case 63675: // Improved Devouring Plague
                 spellInfo->AttributesEx3 |= SPELL_ATTR3_NO_DONE_BONUS;
                 break;