Remove last traces of SCM credential auth from libpq?

Hi all,

libpq has kept some code related to the support of authentication with
SCM credentials for some time now, code dead in the backend since
9.1.  Wouldn't it be time to let it go and remove this code entirely,
erroring in libpq if attempting to connect to a server that supports
that?

Hard to say if this is actually working these days.

Opinions or thoughts?
--
Michael