R1:13ef5c6f2314

When administrators revoke SSH keys, don't include a "security warning" in the mail

Summary:
Depends on D18906. Ref T13043. When SSH keys are edited, we normally include a warning that if you don't recognize the activity you might have problems in the mail body.

Currently, this warning is also shown for revocations with `bin/auth revoke --type ssh`. However, these revocations are safe (revocations are generally not dangerous anyway) and almost certainly legitimate and administrative, so don't warn users…