Use couch_httpd_db:parse_copy_destination_header
Use couch_httpd_db:parse_copy_destination_header

Remove parse_copy_destination_header and use the function defined
in couch_httpd_db instead.

Requires cloudant/dbcore@e9745834c164f6ef7f9e583bc4c36cdd83c415f4
so that parse_copy_destination_header is exported and has the
relevant backported code to throw an HTTP 400 if the COPY request
header does not have a Destination field.

BugzID: 18659

fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb,fkaempfer/couchdb