Truncate very old, overlong Maniphest mail keys

Summary:
Ref T1191. Long ago, Maniphest generated with 40-character mail keys. These prevent the migration to `bytes20`. We had about 300 of these on secure.phabricator.com from several years ago.

Just truncate them. This adjusts reply-to addresses, but it's very likely that none are relevant anymore.

Test Plan: Ran migration on `secure.phabricator.com` to truncate keys.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T1191

Differential Revision: https://secure.phabricator.com/D10615