builtin/history: rename "--ref-action=" to "--update-refs="

builtin/history: rename "--ref-action=" to "--update-refs="

With the preceding commit we have changed "--ref-action=" to only
control which refs are supposed to be updated, not what happens with
them. As a consequence, the option is now somewhat misnamed, as we don't
control the action itself anymore.

Rename it to "--update-refs=" to better align it with its new use.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>