Remove epoll_create1 missing work around

This was introduces in Linux Linux 2.6.27, glibc 2.9 and Android API
level 21.

Since both are equal or lower than our supported versions we don't need
this fallback any longer.

src/sys/unix/selector/epoll.rs

@@ -21,33 +21,10 @@ pub struct Selector {
 
 impl Selector {
     pub fn new() -> io::Result<Selector> {
-        let ep = match syscall!(epoll_create1(libc::EPOLL_CLOEXEC)) {
-            Ok(ep) => ep as RawFd,
-            Err(err) => {
-                // When `epoll_create1` is not available fall back to use
-                // `epoll_create` followed by `fcntl`.
-                if let Some(libc::ENOSYS) = err.raw_os_error() {
-                    match syscall!(epoll_create(1024)) {
-                        Ok(ep) => match syscall!(fcntl(ep, libc::F_SETFD, libc::FD_CLOEXEC)) {
-                            Ok(ep) => ep as RawFd,
-                            Err(err) => {
-                                // `fcntl` failed, cleanup `ep`.
-                                let _ = unsafe { libc::close(ep) };
-                                return Err(err);
-                            }
-                        },
-                        Err(err) => return Err(err),
-                    }
-                } else {
-                    return Err(err);
-                }
-            }
-        };
-
         Ok(Selector {
             #[cfg(debug_assertions)]
             id: NEXT_ID.fetch_add(1, Ordering::Relaxed),
-            ep,
+            ep: syscall!(epoll_create1(libc::EPOLL_CLOEXEC))?,
         })
     }