Remove disable script of firewalld

I get [1] when trying to build a DC/OS image.

+ sudo systemctl disable firewalld
Operation failed: No such file or directory

Change-Id: I94c1d4c8056526502ad4c17af85209388bed8b21

contrib/drivers/dcos_centos_v1/image/dcos/post-install.d/99-disable-firewall

@@ -1,12 +0,0 @@
-#!/bin/bash
-
-if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
-    set -x
-fi
-set -eu
-set -o pipefail
-
-# CentOS-7 introduced firewalld, which is a wrapper around iptables
-# and can conflict with Docker.
-# See https://docs.docker.com/v1.6/installation/centos/#firewalld
-sudo systemctl disable firewalld