R1:5343b1f898d4

Remove defunct "metamta.herald.show-hints" Config option

Summary:
Ref T13216. See PHI985. This config option once controlled adding a Herald transcript link to email. However, this was never implemented in a generic way and was removed from revisions in D8459 and from commits in D10705. No one has noticed or asked for this option for several years, so this is probably a good opportunity to simplify the software and reduce the total amount of configuration.

If we did want to pursue this in the future, I'd…