Fix spy in ManualsController spec
Fix spy in ManualsController spec

This class doesn't appear to be used by RSpec to constrain the method
which can be called on the spy. However, it was misleading for the
spec to suggest that `ManualsController#services` was returning an
instance of a subclass of `AbstractSectionServiceRegistry`.

alphagov/manuals-publisher,alphagov/manuals-publisher,alphagov/manuals-publisher