Issue/pup 2349/cleanup warning during pluginsync

I assume it could, and I toyed with that idea briefly. I opted for this location because it's closer to the `validate` logic, so it would be more resilient to, say, a rewrite of this method that didn't use `Puppet::FileServing::Metadata#mode`. But that may just be overly paranoid of me, and I can certainly see the charms of making it closer to the source of the `mode`.

Thoughts?