destroys (does not retrieve) all entities matching criteria (criteria is optional) returns num of entities deleted to callback
function(criteria, cb) {
        if (_.isFunction(criteria)) { cb = criteria; criteria = undefined; }
        var self = this;
        var query = buildQuery(criteria);
        client.delete(options(self, query), translateSDKCallback(function (err, data) {
          if (err) { return cb(err); }
          cb(null, data.entities.length);
        }));
      }