[core] Remove remaining services

Services are ideally shared across providers so belong as part
of `fog-core` this removes the files that had been left over from
the extraction work.

It also removes the duplicated `require` calls that were in place.

All `fog/{provider}/core` files reference `fog/core` which already
requires the services.

**Note** this may put us out of sync between `fog` and `fog-core`
since fog v1.21.0 is *next* but fog-core v1.21.0 is already out.

I'm not certain if https://github.com/fog/fog-core/pull/14 was part of that release or not.