[misc] PackWorker: drop workaround for db.close in mongojs@1

REF: 3ed3932ee837920e95661b0308dee012f40a71dd

services/track-changes/app/js/PackWorker.js

@@ -78,18 +78,6 @@ logger.log(
   `checking for updates, limit=${LIMIT}, delay=${DOCUMENT_PACK_DELAY}, timeout=${TIMEOUT}`
 )
 
-// work around for https://github.com/mafintosh/mongojs/issues/224
-db.close = function (callback) {
-  return this._getServer(function (err, server) {
-    if (err != null) {
-      return callback(err)
-    }
-    server = server.destroy != null ? server : server.topology
-    server.destroy(true, true)
-    return callback()
-  })
-}
-
 const finish = function () {
   if (shutDownTimer != null) {
     logger.log('cancelling timeout')