Remove the `ArcanistBaseWorkflow::getUserGUID` function.
Remove the `ArcanistBaseWorkflow::getUserGUID` function.

Summary: This function has been deprecated for a long time (see rARC8150fdf044818c503a588c1b3ef0ddbb93cfa1be). It should be safe to remove it now.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley, Korvin

Differential Revision: https://secure.phabricator.com/D9465

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