fx_cast_spell: all casts are instant

bg2 has a few spells with param2 at 0 (contingencies, polymorphs), but
those uses did not impose new casting waits in the original. So we now
treat both "known" param2 values the same. This is not new, just made
explicit for a cleanup
fx_cast_spell_point: never change orientation

next commits will indirectly make it explicitly noninterruptible and instant
no uses in bg2, but now it will match its siblings behaviour
made DirectlyCastSpell* take two parameters less, as all users agree