Moved. Ask your Eluna related questions in Eluna -> SUPPORT not in the 'Lua' release section..
Use the player hook "PLAYER_EVENT_ON_SPELL_CAST" and inside of the function you can check the entry of the spell in an if statement so you know which aura to remove after the player casts a spell "if (spell:GetEntry() == ENTRY) then", then call player":RemoveAura(spellId[, casterGUID])".