Remove remaining instances of St. Edward's Crown

[querkmachine]

What

Remove any remaining files and code associated with the St. Edward's Crown logo.

Note

Updates to the Crown Copyright arms (which also feature St. Edward's Crown) are also anticipated to happen prior to the v6 release. Those changes could be folded into this issue when more is known.

Why

GOV.UK Frontend 5.1 released the new Tudor Crown logo as an opt-in change. A later feature release made this the default, but retained the St. Edward's Crown logo as a deprecated option.

At the next breaking release (presumably v6), the old logo can be removed entirely.

Who needs to work on this

• Developers

Who needs to review this

• Developers

Done when

• The old logo has been removed from the header
  • SVG code removed
  • Nunjucks parameter removed
  • Nunjucks documentation removed
  • Tests removed
• Any other assets remaining have been removed