Remove robots.txt file.

Rummager isn't even a public-facing app any more, so we definitely don't
need this.
Remove the tmp directory.

The only reason for having this around was to be able to restart
Passenger by touching `tmp/restart.txt`. Since we're not using Passenger
any more, there's no reason to keep this directory.
Merge pull request #66 from alphagov/no-robots-file

Remove robots.txt file
Merge pull request #67 from alphagov/no-tmp-directory

Remove the tmp directory