No need to retrieve api key externally, QueryTablesApi takes care

lib/cartodb/server_options.js

@@ -197,31 +197,8 @@ module.exports = function(redisPool) {
             }
             return [req.params.table];
           }
-          var user, key;
+
-          var next = this;
+          queryTablesApi.getAffectedTablesInQuery(that.userByReq(req), sql, this); // in addCacheChannel
-          Step (
-            function findUserKey() {
-              if ( req.params.hasOwnProperty('_authorizedBySigner') ) {
-                user = req.params._authorizedBySigner;
-                cartoData.getUserMapKey(user, this);
-              } else {
-                user = that.userByReq(req);
-                key = req.params.map_key || req.params.api_key;
-                return null;
-              }
-            },
-            function getAffected(err, data) {
-              if ( err ) throw err;
-              if ( data ) {
-                if ( req.profiler ) req.profiler.done('getSignerMapKey');
-                key = data;
-              }
-              queryTablesApi.getAffectedTablesInQuery(user, sql, this); // in addCacheChannel
-            },
-            function finish(err, data) {
-              next(err,data);
-            }
-          );
         },
         function buildCacheChannel(err, tableNames) {
           if ( err ) throw err;