Remove duplicated method for forcing apt-get update.
Remove duplicated method for forcing apt-get update.

This wasn't working in all cases, and has been superceeded by #224

alphagov/ci-puppet,alphagov/ci-puppet,boffbowsh/ci-puppet,alphagov/ci-puppet,alphagov/ci-puppet,boffbowsh/ci-puppet,boffbowsh/ci-puppet,boffbowsh/ci-puppet