R1:1a964f71bb0d

Disable SimpleXML entity loader in Phabricator

Summary: See D8049. Same deal as that one, but this is in the Phabricator web stack.

Test Plan: Man oh man.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Differential Revision: https://secure.phabricator.com/D8050