Remove an unused variable
Remove an unused variable

Summary: Ref T7604. Remove an unused variable from `ArcanistDiffWorkflow`.

Test Plan: This diff, I guess.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Maniphest Tasks: T7604

Differential Revision: https://secure.phabricator.com/D12972

Khan/arcanist,codelabs-ch/arcanist,phacility/arcanist,PageUpPeopleOrg/arcanist-patches,haskell-infra/arcanist,wikimedia/phabricator-arcanist,r4nt/arcanist,jra3/arcanist,hach-que/arcanist,aik099/arcanist,KieranHayes/arcanist,phacility/arcanist,wharris/arcanist,codelabs-ch/arcanist,r4nt/arcanist,chundongwang/arcanist,chundongwang/arcanist,Khan/arcanist,wxstars/arcanist,memsql/arcanist,codelabs-ch/arcanist,jra3/arcanist,phacility/arcanist,fivestars/arcanist,memsql/arcanist,KieranHayes/arcanist,wxstars/arcanist,kevinseelbach/arcanist,zhihu/arcanist,Khan/arcanist,kevinseelbach/arcanist,wharris/arcanist,r4nt/arcanist,wikimedia/phabricator-arcanist,Symplicity/arcanist,hach-que/arcanist,folsom-labs/arcanist,KieranHayes/arcanist,calblueprint/arcanist,haskell-infra/arcanist,fivestars/arcanist,r4nt/arcanist,wxstars/arcanist,wxstars/arcanist,eSpark/arcanist,calblueprint/arcanist,alexmv/arcanist,fivestars/arcanist,zhihu/arcanist,sneakpeeq/arcanist,coursera/arcanist,PageUpPeopleOrg/arcanist-patches,coursera/arcanist,eSpark/arcanist,Symplicity/arcanist,codelabs-ch/arcanist,coursera/arcanist,kevinseelbach/arcanist,phacility/arcanist,sneakpeeq/arcanist,zhihu/arcanist,wharris/arcanist,alexmv/arcanist,Khan/arcanist,folsom-labs/arcanist,memsql/arcanist,KieranHayes/arcanist,uber/arcanist,sneakpeeq/arcanist,Symplicity/arcanist,jra3/arcanist,coursera/arcanist,aik099/arcanist,jra3/arcanist,kevinseelbach/arcanist,hach-que/arcanist,folsom-labs/arcanist,hach-que/arcanist,aik099/arcanist,calblueprint/arcanist,memsql/arcanist,uber/arcanist,phacility/arcanist,alexmv/arcanist,alexmv/arcanist,chundongwang/arcanist,haskell-infra/arcanist,PageUpPeopleOrg/arcanist-patches,eSpark/arcanist,wikimedia/phabricator-arcanist,eSpark/arcanist,Symplicity/arcanist,chundongwang/arcanist,sneakpeeq/arcanist,wharris/arcanist,haskell-infra/arcanist,codelabs-ch/arcanist,aik099/arcanist,PageUpPeopleOrg/arcanist-patches,fivestars/arcanist,folsom-labs/arcanist,wikimedia/phabricator-arcanist,uber/arcanist,calblueprint/arcanist,uber/arcanist,zhihu/arcanist