python: deprecate code formatting messages as text and json

python: deprecate code formatting messages as text and json

This code adds functionality at the python level that is unlikely to
be useful for anyone. Furthermore the python bindings strive to be a
thin wrapper around libnotmuch, so this code will be removed in
notmuch 0.14.

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