Remove logstash mqtt plugin install

The logstash mqtt plugin caused issues in production and we're not going
to use it. We'll be emitting mqtt notifications directly from the
gearman worker instead. So this commit removes the plugin install so we
can set enable_mqtt to true to install the cert.

Change-Id: I0a17444cce18dd4b63f1f924e393483f6d8fe8eb

manifests/indexer.pp

@@ -87,12 +87,6 @@ class logstash::indexer (
     require => Class['logstash'],
   }
   if $enable_mqtt {
-    exec {'install_mqtt_plugin':
-      command => '/opt/logstash/bin/plugin install logstash-output-mqtt',
-      before  => Service['logstash'],
-      unless  => '/opt/logstash/bin/plugin list logstash-output-mqtt',
-    }
-
     file { '/etc/logstash/mqtt-root-CA.pem.crt':
       ensure  => present,
       content => $mqtt_ca_cert_contents,