Update outdated Suite macro documentation

[Wouter01]

Remove the doc stating that the @Suite macro only works on Copyable types.

Motivation:

When reading through the docs, I was quite confused seeing it stated that ~Copyable types aren't supported by the @Suite macro, whereas it does work when doing so. I had a look at it looks like that restriction has been lifted by #619, but the docs weren't updated.

Modifications:

Updated the docs

Checklist:

• Code and documentation should follow the style of the Style Guide.
• If public symbols are renamed or modified, DocC references should be updated.

[stmontgomery]

@swift-ci Please test

[stmontgomery]

Makes sense to me, thanks

[grynspan]

Ship it!