Remove call to "arcanist.projectinfo" from ArcanistWorkflow

Summary: Ref T7604. Remove call to the arcanist.projectinfo Conduit endpoint from ArcanistWorkflow. Depends on D12992.

Test Plan: Ran arc which and verified that repository information was present.

Reviewers: epriestley, Blessed Reviewers

Reviewed By: epriestley, Blessed Reviewers

Subscribers: epriestley

Maniphest Tasks: T7604

Differential Revision: https://secure.phabricator.com/D12971