Remove the `inlines` workflow

Summary: Ref T5112. The `arc inlines` workflow no longer works because the `differential.getrevisioncomments` API method has been deprecated (see T2222). The command is basically useless right now.

Test Plan: N/A

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5112

Differential Revision: https://secure.phabricator.com/D9464