Update patterns.md - remove dead link to B&H patterns

[jpoesen]

The "Pattern Library created by Brighton & Hove City Council" link leads to a 403 Permission Denied page.

@andybroomfield clarified that there is no up-to-date replacement, so I suggest we remove this paragraph altogether.

Related discussion: #259

What does this change?

How to test

How can we measure success?

Have we considered potential risks?

Images

Accessibility

• [ ] Tested with screen reader
• [ ] Navigable with keyboard
• [ ] Colour contrast passed
• [ ] The change doesn't use only colour to convey meaning

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