mailscripts 0.11 now ships a derivative of devel/printmimestructure
called email-print-mime-structure. Maintenance for that utility will
happen in mailscripts from now on, so we should not track an
independent copy of it in notmuch's source tree.
See https://bugs.debian.org/939993 for more details about the
adoption.
Signed-off-by: Daniel Kahn Gillmor <dkg@fifthhorseman.net>