Remove redundant administrator requirement from application edit policy page

Summary:
Fixes T7485. Before applications had proper policies, we gated access by requiring the viewer be an administrator.

This is now redundant (CAN_EDIT on applications has the same effect, and performs the same check), and may some day be wrong (we might let administrators configure a different policy to control who can configure applications). Today, it gets the policy dialog wrong.

Test Plan:
Clicked "Edit Policies" as a non-administrator, was unable to, got nice error:

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T7485

Differential Revision: https://secure.phabricator.com/D12125