Revert "Add dnf to LXC container cache"
Revert "Add dnf to LXC container cache"

This reverts commit 354ed972cd24180270653c88d43fb3748598798a.

CentOS has removed dnf from the EPEL repositories and will have
an updated dnf available for CentOS 7 sometime soon. ☹

Change-Id: I8e4428b2dc54c76cf769954a40bd1790922f976d

openstack/openstack-ansible-lxc_hosts,openstack/openstack-ansible-lxc_hosts