Migrate .arcconfig to mid 2020 changes of "arc land"
Summary: Fixes T27611.
Test Plan: Landing of this revision.
Reviewers: O1 MITK Reviewer Group I, floca
Reviewed By: O1 MITK Reviewer Group I, floca
Maniphest Tasks: T27611
Differential Revision: https://phabricator.mitk.org/D359