tests: move the phabricator auth token to the global config file The next commit introduces a new repo to simplify its development. This value needs to be modified to record tests, so it doesn't make sense to have to do that twice. The callsign and URL are *not* moved because there are tests that fallback to the .arcconfig file when those aren't present. Differential Revision: https://phab.mercurial-scm.org/D8390