Change touch of death from instadeath to maxhp reduction and damage

Touch of death will now do 50 + 8d6 damage, and drain max HP for half
of that. If the drain is equal or greater than your max HP, then it
will kill you instantly.

Change originally from SporkHack by Derek Ray.

src/uhitm.c

@@ -3209,9 +3209,7 @@ mhitm_ad_deth(struct monst *magr, struct attack *mattk UNUSED,
         case 18:
         case 17:
             if (!Antimagic) {
-                g.killer.format = KILLED_BY_AN;
-                Strcpy(g.killer.name, "touch of death");
-                done(DIED);
+                touch_of_death();
                 mhm->damage = 0;
                 return;
             }