puppet-dashboard-workers service cannot be run if passenger is used

If passenger is used, the puppet-dashboard config file (/etc/default/puppet-dashboard in Debian) is declared as being absent. It thus removes the version installed by the package manager.

When using the puppet-dashboard package (1.2.23-1puppetlabs1) from the puppetlabs repo, the /etc/default/puppet-labs-workers file tries to source /etc/default/puppet-dashboard and therefore fails to start.

As the service for puppet-dashboard is (rightfully) disabled in the dashboard::passenger module, it should not be needed to drop the puppet-dashboard default configuration file.