Drop support for `rest-client`

[arielvalentin]

The gem is unmaintained and no longer receiving updates: rest-client/rest-client#830

[github-actions]

👋 This issue has been marked as stale because it has been open with no activity. You can: comment on the issue or remove the stale label to hold stale off for a while, add the keep label to hold stale off permanently, or do nothing. If you do nothing this issue will be closed eventually by the stale bot.