TMP, for test. Revert "Don't use thread::sleep in tests on SGX"

This reverts commit 5c2e1d5.

src/rwlock.rs

@@ -533,15 +533,7 @@ mod tests {
         thread::spawn(move || {
             let _lock = arc2.write();
         });
-
-        if cfg!(not(all(target_env = "sgx", target_vendor = "fortanix"))) {
-            thread::sleep(Duration::from_millis(100));
-        } else {
-            // FIXME: https://github.com/fortanix/rust-sgx/issues/31
-            for _ in 0..100 {
-                thread::yield_now();
-            }
-        }
+        thread::sleep(Duration::from_millis(100));
 
         // A normal read would block here since there is a pending writer
         let _lock2 = arc.read_recursive();