Revert "Install EPEL for os_horizon"

As EPEL is now deployed in the LXC cache and by the pip_install
role, this is no longer required.

This reverts commit 1cdcff81062db2a5bc50a9ba39e7f6d7ee16b011.

Change-Id: I642a36a58831ff1efa73927e09ed6f066b6e5db4

tasks/horizon_install.yml

@@ -44,15 +44,6 @@
     - { src: "/var/log/httpd", dest: "/var/log/apache2" }
   when: ansible_pkg_mgr == 'yum'
 
-# NOTE: The pip_install role configures the RDO repository to be at a higher
-#       priority than EPEL. Packages from RDO will be preferred over EPEL.
-- name: Install EPEL repository
-  yum:
-    name: epel-release
-    state: "{{ horizon_package_state }}"
-  when:
-    - ansible_pkg_mgr == 'yum'
-
 - name: Install distro packages
   package:
     name: "{{ item }}"