Fix breakage of Pholio

Summary: Removal of PholioMockEditor::applyCustomInternalTransaction() in D17868 broke creation of new mocks in Pholio. Puts the empty method back until we finish migrating Pholio to modular transactions.

Test Plan: Created some mocks, observed lack of unhandled exception.

Reviewers: #blessed_reviewers, epriestley

Reviewed By: #blessed_reviewers, epriestley

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D17889