Simplify Writing Tests recipe with hooks

[nickmccurdy]

---

name: "\U0001F4D6 New/Updated Documentation Content"
about: Adding a new docs page, or updating content in an existing docs page

PR Type

Does this PR add a new page, or update an existing page?
Existing

Checklist

• Is there an existing issue for this PR?
  • Add docs for testing Redux with hooks (e.g. useSelector, useDispatch, etc) and React Router and ++ testing-library/testing-library-docs#570
• Have the files been linted and formatted?

What docs page is being added or updated?

• Section: Components and Connected Components
• Page: Writing Tests

For Updating Existing Content

What updates should be made to the page?

The Components and Connected Components sections are merged together, using React Redux hooks as an example of connected components (since they're not usually separate from unconnected components any more). This makes them more consistent with the Testing Library recipe (which I'd like to remove in favor of this one) and easier to understand for new hook-based components.

Do these updates change any of the assumptions or target audience? If so, how do they change?

They assume they're using React 16.8+ with hooks, which should be a fair assumption as the new tutorial already uses it.

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