When SEDUCE is disabled, instead of swapping attacks in mons[] once,
do it on the fly in getmattk() whenever needed. That allows mons[]
to become readonly, although this doesn't declare it 'const' because
doing so will require a zillion 'struct permonst *' updates to match.
This seemed trickier than it should be, but that turned out to be
because the old behavior was broken. Setting SEDUCE=0 in sysconf or
user's own configuration file resulted in all succubus and incubus
attacks being described as monster smiles engagingly or seductively
rather than hitting (while dishing out physical damage). I didn't
try rebuilding 3.4.3 to see whether this was already broken before
being migrated to SYSCF.
b1782b813f