Fix possible stacking exploit of combustion

Prevent keeping mage talent combustion aura and triggered aura when unlearning talents


This commit [4d68c37](http://github.com/mangos-zero/server-old/commit/4d68c37) is one of those pending backports from old mangos-zero concatenated in: https://github.com/cmangos/issues/wiki/classic_backporting-todo-zero-commits

I tested it and this is my report:
> without this fix it is possible to take advantage of the unlearn mechanics to use combustion aura even after unlearning the talent. This commit fixes it.