Make callsigns optional in arcanist
Remove couple of references to callsigns:
- arc which now prints repository name
- getShouldAmend() can now use new format of commit name
a quick git-grep looks like the remaining references are all about repository.callsign config.
- arc which on a repository with no callsign
- trigger requireCleanWorkingCopy(), see both "Do you want to amend this change" and "Do you want to create a new commit" prompts.
- fire this diff with new code.
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Maniphest Tasks: T4245
Differential Revision: https://secure.phabricator.com/D15472