Stop calling the undefined withIsTag method
Summary: This just cleans up a method call that was missed in D15986. It's been causing fatal errors in one of our workflows.
Test Plan: Grep'd for other instances of withIsTag and didn't find any
Reviewers: Blessed Reviewers, epriestley
Reviewed By: Blessed Reviewers, epriestley
Subscribers: epriestley, yelirekim
Differential Revision: https://secure.phabricator.com/D17299