Move gms::arrival_window to api/failure_detector which is its only user.
and get rid of the rest, which is not used, now that we use direct_failure_detector instead.
TODO: integare direct_failure_detector with failure_detector api.
Closes#13576
* github.com:scylladb/scylladb:
gms: get rid of unused failure_detector
api: failure_detector: remove false dependency on failure_detector::arrival_window
test: rest_api: add test_failure_detector