MB-10817: Don't bundle a copy of JSON_checker

Change-Id: I68db4fdd8dd604ee99ba119e0304ed1c824f0613
Reviewed-on: http://review.couchbase.org/35545
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>