Use ActionList-based dropdowns in Conpherence

Summary:
See D8966, D8973. Replace PhabricatorDropdownMenu with PHUIXDropdownMenu.

These new menus look weird on mobile because all action lists pick up a bunch of weird styles on mobile and we're now reusing the CSS.

Test Plan:

Reviewers: btrahan, chad

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8974