Login to Comment - kill intermediary dialogue

Summary: its not necessary. Fixes T5906

Test Plan: clicked "Login to Comment" and went straight to the login form, sans intermediary dialogue

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: epriestley, Korvin

Maniphest Tasks: T5906

Differential Revision: https://secure.phabricator.com/D10295