Revert the private qtcore_unix related changes because they break the Qt 4 build

Revert "Open file descriptors thread-safely on Unix and don't leak them"

This reverts commit 691212d9e492b12590d5b7f4e2b24921911d4b17.

Revert "Protect against EINTR in Unix non-atomic I/O calls"

This reverts commit a8597cbae47076e33b638c2e593f852c8c0a02d5.

Change-Id: I6d931ae6d3b4bee9be019fdf4a08ecc5a41a2b0f
Reviewed-by: Sergey Belyashov <Sergey.Belyashov@gmail.com>