b4: Drop linktrailermask

When grabbing a patch series, the link trailer is replaced with a
Message-ID, which is not useful compared to an URL. Fix that by
dropping the linktrailermask config.

Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Cc: Jiaxun Yang <jiaxun.yang@flygoat.com>
Fixes: 838cf72b5d ("Add a b4 configuration file")
Link: https://lore.kernel.org/qemu-devel/20250630172301.519848-1-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>

.b4-config

@@ -11,4 +11,3 @@
     prep-perpatch-check-cmd = scripts/checkpatch.pl -q --terse --no-summary --mailback -
     searchmask = https://lore.kernel.org/qemu-devel/?x=m&t=1&q=%s
     linkmask = https://lore.kernel.org/qemu-devel/%s
-    linktrailermask = Message-ID: <%s>