Remove an unused function.
Fix a mistake in rebasing.
Remove some unused ABFLAG_s.
Mindexicide: MiscastEffect.

I also cleared out what appeared to be dead code while I was there,
though I may have missed some logical errors, especially with blaming
(for gods etc.). This includes removing MiscastEffect::guilty; it was
used very haphazardly, sometimes being surrounded by uses of act_source,
and I'm not sure that it was ever different.
Remove {target,source}_as_monster.

This will cause a segfault if target is NULL, but it already would
if the result were dereferenced if target were NULL or &you.