Remove Redox OS specific dependency on nix

Author: ChrisDryden

src/uucore/src/lib/features/process.rs

@@ -8,7 +8,6 @@
 // spell-checker:ignore pgrep pwait snice getpgrp
 
 use libc::{gid_t, pid_t, uid_t};
-#[cfg(not(target_os = "redox"))]
 use nix::errno::Errno;
 use std::io;
 use std::process::Child;