python: remove notmuch.py

Removes notmuch.py. If someone wants to step up and work on this it
can always be restored using the version control system.

notmuch.py was meant to be a python implementation of the notmuch
utility. It was never finished and hasn't been updated to changes in
the API and bindings and its features and interface haven't been kept
in sync with the notmuch utility.

Signed-off-by: Justus Winter <4winter@informatik.uni-hamburg.de>