The atomic queue shouldn't use a different atomic class

Even if we're have c++11 atomics the atomic queue would use the
old atomic code. This change makes sure that we use a single
implementation.

Change-Id: Ibf315ece1f34c719e6ff6309d3e9fc68668c1d89
Reviewed-on: http://review.couchbase.org/43073
Reviewed-by: abhinav dangeti <abhinav@couchbase.com>
Tested-by: Michael Wiederhold <mike@couchbase.com>