Remove gendered mons indices from roles, races

There are no longer distinct gendered versions of monsters, so femalenum
is unused (i.e. set to NON_PM) for all roles and races. Take a pass at
removing all uses of/references to femalenum, and rename 'malenum' to
'mnum' since it no longer has any particular association with
gender or sex.

src/mondata.c

@@ -1166,7 +1166,7 @@ const struct permonst *
 raceptr(struct monst* mtmp)
 {
     if (mtmp == &g.youmonst && !Upolyd)
-        return &mons[g.urace.malenum];
+        return &mons[g.urace.mnum];
     else
         return mtmp->data;
 }