Don't create a centos yum repository

This exact repository along with others are part of the
centos cloud image. From the looks of it this was required for
a very early cloud image.

Change-Id: Ib928e4ea739bc48f196f81c96ed4fba3177471f0

elements/centos7/pre-install.d/01-yum-repos

@@ -1,16 +0,0 @@
-#!/bin/bash
-
-if [ ${DIB_DEBUG_TRACE:-0} -gt 0 ]; then
-    set -x
-fi
-set -eu
-set -o pipefail
-
-cat << EOF > /etc/yum.repos.d/centos7-latest.repo
-[centos7]
-name=centos7
-mirrorlist=http://mirrorlist.centos.org/?release=7&arch=\$basearch&repo=os&infra=\$infra
-enabled=1
-metadata_expire=7d
-gpgcheck=0
-EOF