Remove unused argument from ProfileImageWorkflow

Summary: Ref T10319. Removing an unused arg from the workflow script for building profile images.

Test Plan: Rerun bin/people profileimage --users chad 007 --force

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T10319

Differential Revision: https://secure.phabricator.com/D17466