Fixes T4603. We fire arc close-revision --finalize implicitly from arc land, which may close a corresponding Differential revision.
We want to close if the repository is not present in Phabricator (i.e., we'll never be able to close in response to the commit message, since we'll never see it). Historically, we used Arcanist Project -> "Tracked" to make this determination. Instead, just check if the working copy is associated with a repository. This is simpler, easier, and works better.