Update organisation classes

[AshGDS]

What / Why

• Renames two classes in the Whitehall organisation colours model.
• These classes were renamed in govuk-frontend. They did not break when they were renamed, as we had 'middle man'/conversion classes in govuk_publishing_components that would redirect the old class names to the correct class name. However if we update the class in the model, we can then remove those conversion classes from govuk_publishing_components.
• These classes are used for the border colours on the DSIT org page and Office of the Leader of the House of Commons org page.
• This change should be very safe, because:
  • if you inspect element on those organisation pages, and rename the border classes (e.g. brand--department-for-science-innovation-and-technology becomes brand--department-for-science-innovation-technology) the border colours stay the same.
  • These new class names definitely exist in govuk-frontend. See here.
  • We've done this before.
  • The old class names also still exist in the gem, so there's no time pressure to deploy this.
  • Worst case scenario, the border colours would turn black, but I can't see how this would happen.
• This change is a part of some technical debt cleanup as a result of **BREAKING** Refactor organisation styles and upgrade to govuk-frontend v5.7.1 govuk_publishing_components#4321