Revert "Follow notmuch behavior if Message-ID header does not follow spec"

This reverts commit 8565c3a7f319b0baf04185982da61eb86d53d647.

It seems we can ask notmuch to get the generated ID, rather than
duplicate code and generate the ID within mutt.
nomtuch: always use notmuch message ID

It's better to use notmuch message Id than rely on Id from parsed
message, because notmuch ensures that Id exists and it generates
a fake Id for broken messages without the Id.

Reported-by: Michael Zeltner <m@niij.org>
Signed-off-by: Karel Zak <kzak@redhat.com>