Changes for print stylesheets

- Removed the Govspeak styling from print views. The main govspeak
  styling are designed for desktop and not print. They were causing the
  fonts to be far to big and to much spacing.
- Removed print sass helper as it was no longer used.
- Updated the print styles to use the new heading/copy mixins as the
  ig-core mixins are depricated.
- Removed the detailed guide print stylesheet. The main styles are good
  enough and they didn't add anything to the quality of the print
  version.

https://www.pivotaltracker.com/story/show/48728575
Merge pull request #524 from alphagov/print-update

Changes for print stylesheets

https://www.pivotaltracker.com/story/show/48728575