bug#40118: 27.0.90; Signing emails with gpg

[Robert Pluim]

>>>>> On Tue, 05 May 2020 18:06:39 +0300, Eli Zaretskii <eliz@gnu.org> said:

    >> We can do that as well, and put the querying code in master. Eli?

    Eli> Can you show me the changes for emacs-27, please?

    Eli> Thanks.

* lisp/gnus/mml-sec.el (mml-secure-epg-sign): Partially revert
"Make mml-secure-epg-sign bug out if we can't find an identity".
It causes signing to fail for people who have not set up
mml-secure-{smime,openpgp}-sign-with-sender, which is a regression
from Emacs-26 (Bug#40118).

Do not merge to master.
        
diff --git a/lisp/gnus/mml-sec.el b/lisp/gnus/mml-sec.el
index 740e1d2b72..8d77916e99 100644
--- a/lisp/gnus/mml-sec.el
+++ b/lisp/gnus/mml-sec.el
@@ -944,16 +944,6 @@ mml-secure-epg-sign
         (signer-names (mml-secure-signer-names protocol sender))
         (signers (mml-secure-signers context signer-names))
         signature micalg)
-    (unless signers
-      (let ((maybe-msg
-             (if mml-secure-smime-sign-with-sender
-                 "."
-               "; try setting `mml-secure-smime-sign-with-sender'.")))
-        ;; If `mml-secure-smime-sign-with-sender' is already non-nil
-        ;; then there's no point advising the user to examine it.  If
-        ;; there are any other variables worth examining, please
-        ;; improve this error message by having it mention them.
-        (error "Couldn't find any signer names%s" maybe-msg)))
     (when (eq 'OpenPGP protocol)
       (setf (epg-context-armor context) t)
       (setf (epg-context-textmode context) t)