Remove minor version pining

Author: hgreebe

cookbooks/aws-parallelcluster-platform/files/ami_cleanup.sh

@@ -8,6 +8,7 @@ rm -rf /etc/ssh/ssh_host_*
 rm -f /etc/udev/rules.d/70-persistent-net.rules
 grep -l "Created by cloud-init on instance boot automatically" /etc/sysconfig/network-scripts/ifcfg-* | xargs rm -f
 rm -rf /var/crash/*
+rm -f /etc/yum/vars/releasever
 
 # https://bugs.centos.org/view.php?id=13836#c33128
 source /etc/os-release