Don't use obsolete In-Reply-To format in messages (Bug#64454)

Don't use obsolete In-Reply-To format in messages (Bug#64454)

When creating a new message, message-send-mail uses an obsolete format
for the In-Reply-To header that includes additional information about
the originating message.  This patch changes the default to use the
rfc5322 approved format, but allow the obsolete format through a
defcustom.

* lisp/gnus/message.el (message-make-in-reply-to): Return only the
message-id of the originating message (the default) unless the new
custom variable message-header-use-obsolete-in-reply-to is non-nil.
* doc/misc/message.texi: Document the new custom variable
message-header-use-obsolete-in-reply-to.
* etc/NEWS: Update NEWS.

(cherry picked from commit 2eb6171ec96eac0c78cf20b3003fcbcb1206c8c7)