Remove incorrect doc comment about vb arg to HashTable ctor.

Change-Id: Ied5466a2e070bc531b6619307e81b9f3f017d9a5
Reviewed-on: http://review.couchbase.org/34240
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: buildbot <build@couchbase.com>
Tested-by: Chiyoung Seo <chiyoung@couchbase.com>