Only include files used by the crate

[kornelski]

The libz-sys crate is 4MB large, but it only uses 1/10th of the data it bundles.

The zlib repo has all kinds of irrelevant files: a PDF documentation, support files for dead platforms, multiple build C systems, interfaces for various other languages, tests and support utilities. None of that is used by the sys crate.

Also the CVE-2024-3094 has demonstrated that seemingly standard and innocent files like configure and test fixtures can be used to hide malware. While I don't expect libz to do such thing, it is better to have fewer obscure files in the crate, so that it's easier to review.

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I haven't done the same for the zlib-ng crate, because it uses CMake and it's harder to see which files it uses. It might be better to switch it to the cc crate first.

[kornelski]

The CI failures seem to be only caused by network flakiness:

fatal: unable to access 'https://github.com/madler/zlib/': Recv failure: Connection was reset

[Byron]

Thanks a lot, that's a great catch!

I will merge this once CI is green, I restarted it, and also would expect it to work now.