Use epoll_create() directly instead of probing for epoll_create1()

At runtime mio tries to figure out whether to use syscall
epoll_create1() or epoll_create().  However, the Android 4.4 loader
crashes while looking up a symbol that does not
exist (epoll_create1).

More details covered here:
https://users.rust-lang.org/t/libc-dlsym-crashing-on-i686-linux-android/14788

This problem is resolved upstream by commit 479ae7c5e2 ("Cleanup of
sys::unix (#1005)"), but is not yet released officially.

Signed-off-by: Curt Brune <curt@signal.org>

src/sys/unix/epoll.rs

@@ -30,21 +30,9 @@ pub struct Selector {
 impl Selector {
     pub fn new() -> io::Result<Selector> {
         let epfd = unsafe {
-            // Emulate `epoll_create` by using `epoll_create1` if it's available
-            // and otherwise falling back to `epoll_create` followed by a call to
-            // set the CLOEXEC flag.
-            dlsym!(fn epoll_create1(c_int) -> c_int);
-
-            match epoll_create1.get() {
-                Some(epoll_create1_fn) => {
-                    cvt(epoll_create1_fn(libc::EPOLL_CLOEXEC))?
-                }
-                None => {
-                    let fd = cvt(libc::epoll_create(1024))?;
-                    drop(set_cloexec(fd));
-                    fd
-                }
-            }
+            let fd = cvt(libc::epoll_create(1024))?;
+            drop(set_cloexec(fd));
+            fd
         };
 
         // offset by 1 to avoid choosing 0 as the id of a selector