Don't override the mosquitto log path

For unidentified reasons, mosquitto is unable to log to
/var/log/mosquitto.log when running as root but will happily log to
/var/log/mosquitto/mosquitto.log. Luckily that's already the
default in our Puppet module, so just drop the unwarranted override.

Change-Id: Ifbd39b280f089b9e18bfe8e372f180bb8ad4d1e4

modules/openstack_project/manifests/firehose.pp

@@ -25,7 +25,6 @@ class openstack_project::firehose (
 ) {
   include mosquitto
   class {'mosquitto::server':
-    log_file               => '/var/log/mosquitto.log',
     infra_service_username => $mqtt_username,
     infra_service_password => $mqtt_password,
   }