Remove deprecated javelin_render_tag() and phabricator_render_form()

Summary:
Not removing `phutil_render_tag()` for now as it is still used in Diviner.

@edward, please verify Facebook callsites.

Test Plan: Searched for it.

Reviewers: edward, epriestley

Reviewed By: epriestley

CC: aran, Korvin, wez

Differential Revision: https://secure.phabricator.com/D6494