obsolete aggravation comment

Get rid of the obsolete comments about summon spells also aggravating.

The effect on balance of not aggravating is negligible, because nasty() already
wakes up most of the monsters it creates.

src/mcastu.c

@@ -91,7 +91,7 @@ int spellval;
     case 17:
     case 16:
     case 15:
-	return MGC_SUMMON_MONS;	/* also aggravates */
+	return MGC_SUMMON_MONS;
     case 14:
     case 13:
 	return MGC_AGGRAVATION;
@@ -355,7 +355,7 @@ int spellnum;
 	} else
 	    impossible("bad wizard cloning?");
 	break;
-    case MGC_SUMMON_MONS:		/* also aggravates */
+    case MGC_SUMMON_MONS:
     {
 	int count;