apache confs for nagios.* are no more needed

We used to have two virtual hosts nagios.wikimedia.org and
nagios3.wikimedia.org to expose our Nagios installation. We have since
migrated to Icinga for which the virtual host configuration honor
nagios.wikimedia.org requests:

templates/apache/sites/icinga.wikimedia.org.erb

nagios3.wikimedia.org seems to have been an experimentation before we
took the decision to move to Icinga. Seems it is unneeded anymore.

Change-Id: I6be9b96b009642a6c6a3d78e161ba91bb7ac8833
Merge "apache confs for nagios.* are no more needed" into production