coredump: remove duplicate MESSAGE= prefix from message

coredump: remove duplicate MESSAGE= prefix from message

systemd-coredump[9982]: MESSAGE=Process 771 (systemd-journal) of user 0 dumped core.
systemd-coredump[9982]: Coredump diverted to /var/lib/systemd/coredump/core...

log_dispatch() calls log_dispatch_internal() which calls write_to_journal()
which appends MESSAGE= on its own.

(cherry picked from commit 4f62556d71206ac814a020a954b397d4940e14c3)
(cherry picked from commit 9f564b3f45008c1a178a186f944ddc7485614cd2)

Gbp-Pq: Name coredump-remove-duplicate-MESSAGE-prefix-from-message.patch