R1:f705c978b5d7

render_tag -> tag: phabricator_render_form -> phabricator_form

Summary: Convert most phabricator_render_form callsites. In the case of the "headsup view", it converts it by deleting the element entirely (this is the very old Maniphest/Differential header which we no longer use).

Test Plan: Poked around a bit.

Reviewers: vrana

Reviewed By: vrana

CC: aran

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4726