Remove legacy manifests.d/vagrant-managed.pp

The modern MediaWiki-Vagrant uses hiera to manage applied roles and
includes configuration to install role::labs_initial_content when the
"labs" environment is used.

Change-Id: I811c40e5d0db65d55f786bdec4e4b1bf44c863d4
Merge "Remove legacy manifests.d/vagrant-managed.pp" into production