Fix failing tests on orgs_sites_hosts_spec and site_yaml_file_spec

- Use `=~` instead of `eql`, because RSpec was comparing an array to a
  CollectionProxy object. Using `=~` makes it compare just the values,
  e.g. 1 == 1, therefore they're actually the same values.
- Thanks to rgarner for the `=~` tip, and https://github.com/alphagov/transition/commit/77ff1686c0271158f315bcbc851a032a141b0362.
We no longer need to patch action_controller/template_assertions.rb

- Rails 4 implements the things we needed to backport to Rails 3.
Remove attr_accessible from the user model

- This uses Whitehall's implementation of overriding attr_accessible,
  because Rails 4 errors when it encounters attr_accessible, but the
  gds-sso gem is still using attr_accessible. Found through jennyd and
  https://github.com/alphagov/whitehall/blob/11b5293230c318ebca3444b5bc700841ca4810f6/lib/attr_accessible_noop.rb.