CCBC-485: Undocument 'ssl' and 'ca_path' from cntl_string

These two settings are no longer modifiable as of the 2.4 beta version

Change-Id: I7c79fdfc9a4cc1fc23022be51f55a38f164b5a0f
Reviewed-on: http://review.couchbase.org/40055
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Subhashni Balakrishnan <b.subhashni@gmail.com>