Revert "Merge pull request #629 from alphagov/make-sorn-beta-primary-option"

This reverts commit be05d8d79fbde1be0263f20204c77d774d45e6ff, reversing
changes made to e88c9e48daab5675b5b935e9db3530b74aa7694b.

DVLA have requested that this isn't deployed to production yet
Merge pull request #634 from alphagov/revert-sorn-page-update

Revert SORN page update from #629