Remove unused Blob New() method

Code cleanup - no-one uses this method so delete it.

Change-Id: I10df43e052a96832fe9b4c882be6a19497392d38
Reviewed-on: http://review.couchbase.org/42775
Reviewed-by: Sundararaman Sridharan <sundar@couchbase.com>
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: abhinav dangeti <abhinav@couchbase.com>