Always run pulpcore-manager migrate

Pulpcore uses post migration hooks to create data in the database, which
sometimes changes even if there are no real migrations to be run.

This is fine from a Django PoV -- post migration hooks run after every
`migrate` call, even if there have been no changes.

However, this means that we need to run `migrate` unconditionally as
otherwise we might miss changes to the hooks (or their data) when there
is no migration attached.

An example of such a change is
pulp/pulpcore@20cffca
where a new role was introduced and our setup started failing as it was
expecting the role to exist after the upgrade, but it did not as we did
not call `migrate`.

manifests/database.pp

@@ -30,7 +30,6 @@
 
   pulpcore::admin { 'migrate --noinput':
     timeout     => $timeout,
-    unless      => 'pulpcore-manager migrate --check',
     refreshonly => false,
   }