Revert "Link to fast-glob instead of glob in docs (#6333)"

[fisker]

Revert #6333, fixes #6719

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[brodybits]

After another look at PR #6333, I am not 100% convinced reverting it is 100% what we want.

The point of PR #6333 is that the document referred to the glob syntax from node-glob, while we are now using whatever glob syntax is supported by globby.

I think we also do not want to point to the README on the master branch of the globby project, since its readme now refers to fast-glob.

I wonder if we should point to something like https://github.com/sindresorhus/globby/blob/v6.1.0/readme.md#globbing-patterns until we are ready to use globby@10.

Or maybe it is time to stop supporting old installations (Node.js 6 from GitHub) and use globby@latest?

Food for thought.