Jetpack: Remove deprecated jetpack_require_lib and friends

[anomiex]

Proposed changes:

We announced back in 11.6 that these were going to go away in 11.9. It's now time for 11.9, so let's remove them.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

p9dueE-5EZ-p2
#27273

Does this pull request change what data or activity we track or use?

No

Testing instructions:

• Everything should continue to work.

[github-actions]

Thank you for your PR!

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Jetpack plugin:

• Next scheduled release: March 7, 2023.
• Scheduled code freeze: February 28, 2023.

[github-actions]

Are you an Automattician? You can now test your Pull Request on WordPress.com. On your sandbox, run

bin/jetpack-downloader test jetpack remove/deprecated-jetpack_require_lib

to get started. More details: p9dueE-5Nn-p2

[mehdi-nexstar]

The alternative way of using libraries :
require_once JETPACK__PLUGIN_DIR . '_inc/lib/LIB_NAME';