Revert "xz: Use pipe2() if available."

This reverts commit 7a11c4a8e5e15f13d5fa59233b3172e65428efdd.
It is a problem when libc has pipe2() but the kernel is too
old to have pipe2() and thus pipe2() fails. In xz it's pointless
to have a fallback for non-functioning pipe2(); it's better to
avoid pipe2() completely.

Thanks to Michael Fox for the bug report.
2 files changed