Remove redundant condition from case statement
Remove redundant condition from case statement

As far as I can see `ManualsPublisher.document_services` is now only
ever invoked from the `bin/republish_withdrawn_document` script. The
value of the `document_type` argument passed into it is always obtained
from a call to `SpecialistDocumentEdition#document_type`
which will never be 'manual_document'; only 'manual' or one of the
Specialist Document document types, e.g. 'cma_case'. Indeed since this
commit [1], it will only ever be 'manual'. Thus it's safe to remove
this condition.

[1]: 723ce320c9845003bf1aa584d4ea726b587c1891

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