Fixed a memory leak in achievementremove

Fixes #2313

Thanks to @CairoLee

src/map/achievement.c

@@ -131,6 +131,7 @@ bool achievement_remove(struct map_session_data *sd, int achievement_id)
 	if (i != sd->achievement_data.count - 1)
 		memmove(&sd->achievement_data.achievements[i], &sd->achievement_data.achievements[i + 1], sizeof(struct achievement) * (sd->achievement_data.count - 1 - i));
 
+	aFree(&sd->achievement_data.achievements[sd->achievement_data.count-1]);
 	sd->achievement_data.count--;
 	if (!sd->achievement_data.achievements[i].completed)
 		sd->achievement_data.incompleteCount--;