Remove ally/summon XP penalty (in a better way)

Instead of messing around with the XP calculations, just set the
multiplier on pet damage to be the same as all other forms of player
damage. Should be less crashing issues with this version.

crawl-ref/source/mon-death.cc

@@ -700,8 +700,9 @@ int exp_rate(int killer)
     if (killer == MHITYOU || killer == YOU_FAULTLESS)
         return 2;
 
+    //TODO: Consolidate all of this later now that it all returns the same
     if (_is_pet_kill(KILL_MON, killer))
-        return 1;
+        return 2;
 
     return 0;
 }