emacs: Drop content-free "Unknown signature status" button

[notmuch] / test / emacs-show.expected-output / notmuch-show-decrypted-message-no-crypto

test_suite@notmuchmail.org (2000-01-01) (encrypted inbox)
Subject: Here is the password
To: test_suite@notmuchmail.org
Date: Sat, 01 Jan 2000 12:00:00 +0000

[ multipart/encrypted ]
[ Unknown encryption status ]
[ application/pgp-encrypted ]
[ application/octet-stream ]