Remove unneccesssary checks for valid opaque

We do the same check that validateOpaue does right after this and
there is no need to do it twice.

Change-Id: If45cd12bf78b4a0490da001d432882f63c30e7e3
Reviewed-on: http://review.couchbase.org/37917
Reviewed-by: Sriram Ganesan <sriram@couchbase.com>
Reviewed-by: Chiyoung Seo <chiyoung@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>