puppet: Remove zulip::nagios class.

93f62b999e removed the last file in
puppet/zulip/files/nagios_plugins/zulip_nagios_server, which means the
singular rule in zulip::nagios no longer applies cleanly.

Remove the `zulip::nagios` class, as it is no longer needed.

puppet/zulip/manifests/nagios.pp

@@ -1,15 +0,0 @@
-# This manifest installs Zulip's Nagios plugins intended to be on
-# localhost on a Nagios server.
-#
-# Depends on zulip::profile::base to have installed `monitoring-plugins-basic`.
-class zulip::nagios {
-  file { "${zulip::common::nagios_plugins_dir}/zulip_nagios_server":
-    require => Package[$zulip::common::nagios_plugins],
-    recurse => true,
-    purge   => true,
-    owner   => 'root',
-    group   => 'root',
-    mode    => '0755',
-    source  => 'puppet:///modules/zulip/nagios_plugins/zulip_nagios_server',
-  }
-}

puppet/zulip_ops/manifests/profile/nagios.pp

@@ -1,7 +1,6 @@
 class zulip_ops::profile::nagios {
   include zulip_ops::profile::base
   include zulip_ops::apache
-  include zulip::nagios
 
   $nagios_packages = [# Packages needed for Nagios
                       'nagios3',