R1:2e19b78b8dd6

Don't publish anything for "Disable Mail" / "Enable Mail" on projects

Summary:
Fixes T10466. Currently, clicking "Disable Mail" or "Enable Mail" on a project toggles an edge, but it gets a default "added an edge" story and transaction record.

These are confusing, useless and not interesting, so just hide them.

Test Plan:
- Before patch: clicked enable/disable mail, saw "added an edge" / "removed an edge" stories in feed and project history.
- After patch: clicked enable/disable mail, saw nothing in…