units: unify deps between service and socket units

units: unify deps between service and socket units

The current arrangement of service and socket units is
sort of all over the place. Let's clean it up a little,
roughly following the principles below:

- socket units have implicit ordering deps (not to be confused
  with default ones which are subject to DefaultDependencies=)
  before associated service, so drop any explicit After=

- If socket can be enabled, remember to link to it in service
  via Also= and Sockets= (the latter replaces Wants=).
  If the service Requires= socket however, Sockets= is omitted.

- If socket is statically enabled, no need for service
  to pull it in - machined