[Hotfix] remove cruft and symlink pentest env

this is a housecleaning MR that accomplishes the following cleanup tasks:

• remove crufty conf files
  • we no longer use signal-cli or supervisord
  • let's remove their conf files so they don't confuse new devs!
• remove db/backfills
  • we don't actually use any of these scripts; we instead accomplish backfills via migrations
  • let's delete this dir so that devs trying to figure out how to use migrations don't look here!
• add symlink from ansible/files to .env.pentest
  • this will come in handy when we redeploy the pentest server!