test.os: removed io_uring_submit & io_uring_wait_cqe and using

`io_uring_submit_and_wait_timeout`. Was submitting `2 `entries but only
waiting for `1` to complete! now it waits for both to finish.

test/os/unlink_test.py

@@ -26,8 +26,7 @@ def test_unlink(tmp_dir, ring, cqe):
     liburing.io_uring_prep_unlink(sqe, dir_path, liburing.AT_REMOVEDIR)
     sqe.user_data = 2
 
-    assert liburing.io_uring_submit(ring) == 2
-    assert liburing.io_uring_wait_cqe(ring, cqe) == 0
+    assert liburing.io_uring_submit_and_wait_timeout(ring, cqe, 2) == 2
 
     for i in range(2):
         assert liburing.trap_error(cqe[i].res) == 0
@@ -60,8 +59,7 @@ def test_unlinkat(tmp_dir, ring, cqe):
     liburing.io_uring_prep_unlinkat(sqe, dir_path, liburing.AT_REMOVEDIR)
     sqe.user_data = 2
 
-    assert liburing.io_uring_submit(ring) == 2
-    assert liburing.io_uring_wait_cqe(ring, cqe) == 0
+    assert liburing.io_uring_submit_and_wait_timeout(ring, cqe, 2) == 2
 
     for i in range(2):
         assert liburing.trap_error(cqe[i].res) == 0