Stop overriding rsyslog message size on slaves.

* modules/jenkins/manifests/slave.pp: Remove the configuration
snipped and package reload mechanism for rsyslog now that we're back
to using screen logs for devstack-gate.

Change-Id: I328aed006c9f23a4e4dd459b55fc8fcd844f40fa
Reviewed-on: https://review.openstack.org/22654
Reviewed-by: Clark Boylan <clark.boylan@gmail.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins