Revert #3224 jsobfu string size fixes

So my fixes for string chunking in #3224 (primarily changing to short var names) sometimes causes scoping issues with how I was renaming vars. I was not very explicit with the testing instructions, and these changes will often affect how Firefox interprets os.js. So I am reverting this for now, and this needs to land ASAP as I managed to break BAP/BES on master.

Note that I am not reverting the move to the rkelly-remix gem, as that didn't cause any problems AFAICT.

Verification
- [x] get a shell from `exploit/multi/browser/firefox_proto_crmfrequest` on Firefox < 16
- [x] ensure your browser correctly parses the page served by browser_autopwn (you should see no errors in the console)