migration: Drop unused parameter for migration_tls_get_creds()

It is not needed since we moved the accessor for tls properties to
options.c.

Suggested-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
1 file changed