[exim] strip incoming messages of A-R headers that claim to …

Hello list,

I am trying to implement ARC in our Exim setup. While reading
experimental-spec.txt[1] I noticed the follwing: "Note that it would
be wise to strip incoming messages of A-R headers that claim to be
from our own <admd-identifier>." I have some difficulty with realizing
this. I tried a few things and the closest I got to something working
is:

TEST = ${filter{$lheader_Authentication-Results:}{!match{$item}{^our-admd-identifier;}}}

headers_remove Authentication-Results
headers_add Authentication-Results TEST

This solution does not seem to work in all situations, is there a
better way to strip the incoming message of A-R headers that claim to
be from our own admd?

[1] https://github.com/Exim/exim/blob/b07d141af23f2ab160eba2b58a834baee513b3f8/doc/doc-txt/experimental-spec.txt#L515