why-error.md: Remove 1 test

[oech3]

This file should be generated from somewhere.

[github-actions]

GNU testsuite comparison:

GNU test failed: tests/sort/sort-stale-thread-mem. tests/sort/sort-stale-thread-mem is passing on 'main'. Maybe you have to rebase?
Congrats! The gnu test tests/sort/sort-debug-keys is no longer failing!

[cakebaker]

Thanks!

This file should be generated from somewhere.

An alternative is to remove this file (and why-skip.md) and handle it in the issues.

[oech3]

An alternative is to remove this file (and why-skip.md) and handle it in the issues.

@sylvestre OK?

[sylvestre]

Yes thanks

[oech3]

#9835