Remove call to "arcanist.projectinfo" from arc export

Summary:
Ref T7604. Remove a call to arcanist.projectinfo from arc export. This Conduit call was only used to detect the repository encoding, which we should be able to do locally anyway.

I was considering removing the $projectName from ArcanistBundle as well, but I'm not convinved that this is a good idea. Specifically, doing so would make it difficult to issue the "This patch is for the 'X' project, but the working copy belongs to the 'Y' project" error. We could potentially use the repository callsign for this purposes, but this isn't portable across installs.

Test Plan: I'm not quite sure how to test this. I suspect that this functionality isn't widely used anyway.

Reviewers: Blessed Reviewers, epriestley

Reviewed By: Blessed Reviewers, epriestley

Subscribers: Korvin, epriestley

Maniphest Tasks: T7604

Differential Revision: https://secure.phabricator.com/D12962