B OpenNebula/one#4003: RN for #4003, drop C8 openpgm mention (#855)

(cherry picked from commit 4033571)

source/deployment/opennebula_installation/frontend_installation.rst

@@ -94,17 +94,6 @@ Install OpenNebula
 
 Install the CentOS/RHEL OpenNebula Front-end with packages from **our repository** by executing the following as root:
 
-.. note::
-
-   On CentOS/RHEL 8, the essential packages ``openpgm`` and ``openpgm-devel``
-   are still part of the EPEL testing repository, which is not enabled
-   by default. Before installing OpenNebula, you have to first install
-   these packages by running;
-
-   .. prompt:: bash # auto
-
-       # yum install --enablerepo=epel-testing openpgm openpgm-devel
-
 .. prompt:: bash # auto
 
     # yum install opennebula-server opennebula-sunstone opennebula-ruby opennebula-gate opennebula-flow