Components: refactor useFlex to pass exhaustive-deps

[chad1008]

What?

Updates the useFlex hook to pass the exhaustive-deps eslint rule.

Why?

Part of the effort in #41166 to apply exhuastive-deps to the Components package

How?

Removing isReverse from the dependency array, and then because it isn't used anywhere else in the hook, removing the variable entirely.

When this dependency was added, isReverse was used in several places for the creation of the classes object, but the hook has been refactored since then, removing any use of the isReverse variable in the hook.

Based on that, I think this dependency and variable just got left in - removing them doesn't cause any unexpected changes that I can see in Storybook.

cc @sarayourfriend: do you have any thoughts on drawbacks to this approach? If we do, in fact, still need to watch this variable and update the useMemo value when it changes, we'll need to either disable the exhuastive-deps check, or find another approach. Curious what you think 🙂

Testing Instructions

1. From your local Gutenberg directory, run npx eslint --rule 'react-hooks/exhaustive-deps: warn' packages/components/src/flex
2. Confirm that the linter returns no errors
3. Confirm navigation unit tests still pass
4. Run Storybook locally, confirm the Flex component stories and/or docs still work as expected

[codesandbox]

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[sarayourfriend]

This seems like it should be fine. Because direction is already a dependency the styles will get recalculated anyway so the dependency on isReverse wasn't actually doing anything (as far as I can tell), not even in a hacky, sneaky way.

[chad1008]

thanks @sarayourfriend!