Stop using SPELLS_CHANGED event

[mbattersby]

SPELLS_CHANGED is no longer a rare event. Whether by bug or design in Torghast it is being triggered every 0.5 seconds.

See AdiAddons/AdiButtonAuras#388

This is far too often for a complete rescan of the spellbooks.

[Rainrider]

The event is used to be seldom enough with some rare occasions when it was spammer. I recall it fired more often for warlocks probably because of some pet mechanic. Torghast seems to be an odd one in this regard. From my test the spam starts when the extra ability becomes empowered and only while this state persist. Once the player uses the ability, the spam stops until the next empowerment. I will test more why a change is reported by LSB in this case because this triggers rules rebuild for ABA.