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/mplayer.c

@@ -366,8 +366,7 @@ mplayer_talk(register struct monst* mtmp)
     if (mtmp->mpeaceful)
         return; /* will drop to humanoid talk */
 
-    pline("Talk? -- %s", (mtmp->data == &mons[g.urole.malenum]
-                          || mtmp->data == &mons[g.urole.femalenum])
+    pline("Talk? -- %s", mtmp->data == &mons[g.urole.mnum]
                              ? same_class_msg[rn2(3)]
                              : other_class_msg[rn2(3)]);
 }