Remove `differential.anonymous-access`

Summary:
Fixes T3034. This is obsoleted by modern policies.

This was written by a Facebook intern and is rarely used -- the Hive install might be the only use in the wild. It has never really worked correctly.

Test Plan: `grep`; browsed Differential.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T3034

Differential Revision: https://secure.phabricator.com/D7568