R1:a22ef4e9b472

Kill most of phutil_escape_html()

Summary:
This resolves lots of double escaping.
We changed most of `phutil_render_tag(, , $s)` to `phutil_tag(, , $s)` which means that `$s` is now auto-escaped.
Also `pht()` auto escapes if it gets `PhutilSafeHTML`.

Test Plan: None.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, Korvin

Maniphest Tasks: T2432

Differential Revision: https://secure.phabricator.com/D4889