Remove __getitem__/__setitem__ accessors

These are oversimplified and undocumented

Change-Id: Idbea320c9ea601a8a26ef0fa6d657cd748b3ebfd
Reviewed-on: http://review.couchbase.org/41309
Reviewed-by: Dave Rigby <daver@couchbase.com>
Reviewed-by: Volker Mische <volker.mische@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>