Properly implement projectile non-sprite targeting

[lynxlynxlynx]

inareans.pro is supposed to target just non-actors, which we currently work around and then also use the same projectile just as an inarea without affecting the center.

• check which all spells are using inareans
  • replace use in turn.spl
  • replace in any others
  • remove bg1 projectile alias 79dc90c if no users of it left (currently known: turn)
• add code to SecondaryProjectile
  • remove current ignore-center hack for find traps
• simplify fx_find_traps and remove TODO