Remove all edge events

Summary:
Ref T5245. These were a bad idea.

We no longer need actors for edge edits either, so remove those. Generally, edges have fit into the policy model as pure/low-level infrastructure, and they do not have any policy or capability information in and of themselves.

Test Plan: grep

Reviewers: chad, btrahan, joshuaspence

Reviewed By: joshuaspence

Subscribers: epriestley

Maniphest Tasks: T5245

Differential Revision: https://secure.phabricator.com/D9840