Remove gitbook

[digitalfrost]

The open-source development of Gitbook has ceased: see deprecation warning:
https://github.com/GitbookIO/gitbook/blob/master/README.md
and GitbookIO/gitbook#2219 for more details.

Please confirm this pull request meets the following requirements:

• I followed the contributing guidelines: https://github.com/github/explore/blob/main/CONTRIBUTING.md.
• I have no affiliation with the project I am suggesting (as a maintainer, creator, contractor, or employee).

Which change are you proposing?

• Suggesting edits to an existing topic or collection
• Curating a new topic or collection
• Something that does not neatly fit into the binary options above

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Editing an existing topic or collection

I'm suggesting these edits to an existing topic or collection:

• Image (and my file is *.png, square, dimensions 288x288, size <= 75 kB)
• Content (and my changes are in index.md)

Please replace this line with an explanation of why you think these changes should be made.

Curating a new topic or collection

• I've formatted my changes as a new folder directory, named for the topic or collection as it appears in the URL on GitHub (e.g. https://github.com/topics/[NAME] or https://github.com/collections/[NAME])
• My folder contains a *.png image (if applicable) and index.md
• All required fields in my index.md conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

Please replace this line with an explanation of why you think this topic or collection should be curated.

Something that does not neatly fit into the binary options above

• My suggested edits are not about an existing topic or collection, or at least not a single one
• My suggested edits are not about curating a new topic or collection, or at least not a single one
• My suggested edits conform to the Style Guide and API docs: https://github.com/github/explore/tree/main/docs

Please replace this line with an explanation of your proposed changes.

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Please note: we will close your PR without comment if you do not check the boxes above and provide ALL requested information.

[digitalfrost]

Test fails on

Error: expected collection changes to have been appended to the existing item list

My pull request removes an item from the collection... so it is to be expected that this test would fail...

[kenyonj]

We systematically remove repositories when they become unavailable, either through complete removal or being made private. For deprecated or even archived repositories, they are still useful resources in our collections and we leave them in place.

[digitalfrost]

I don't think Github is trying to showcase abadonware in it's Explore tab.
If you think this is valuable it should be moved to another Collection.
Surely the purpose of the made-in-countryX collections is to showcase vibrant and dynamic open source projects which Github users would want to contribute to or use.