remove(connection) {
        for (let i = this._pool.length - 1; i >= 0; i--) {
            if (this.sameConnection(connection, this._pool[i][0])) {
                return this._pool.splice(i, 1)[0][1];
            }
        }
    }
Remove connection from pool
@param {object} connection  Connection object
@returns {*} removed client (or undefined, if no client was found)