promisor-remote: remove the 'accepted' strvec

promisor-remote: remove the 'accepted' strvec

In a previous commit, filter_promisor_remote() was refactored to keep
accepted 'struct promisor_info' instances alive instead of dismantling
them into separate parallel data structures.

Let's go one step further and replace the 'struct strvec *accepted'
argument passed to filter_promisor_remote() with a
'struct string_list *accepted_remotes' argument.

Signed-off-by: Christian Couder <chriscool@tuxfamily.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>