fix test for file send

The test is broken because we can't really guarantee that the old fd
will fail to open. It is entirely possible that by now, some other test
(remember tests are threaded) have opened a new file for itself that
ended up with the same fd as original_fd.

This test was always failing for me when I ran "cargo test" but always
succeeding if I ran the test in isolation, which confirms that this is
the likely cause.

glommio/src/io/dma_file.rs

@@ -780,7 +780,6 @@ pub(crate) mod test {
     };
     use futures::join;
     use futures_lite::{stream, StreamExt};
-    use nix::fcntl::{fcntl, FcntlArg::F_GETFD};
     use rand::{seq::SliceRandom, thread_rng};
     use std::{cell::RefCell, convert::TryInto, path::PathBuf, time::Duration};
 
@@ -1547,8 +1546,6 @@ pub(crate) mod test {
         .join()
         .unwrap();
 
-        assert_eq!(fcntl(original_fd, F_GETFD), Err(nix::errno::Errno::EBADF));
-
         let file: DmaFile = result.into();
         assert_ne!(file.as_raw_fd(), original_fd);
         assert_eq!(file.file.inode, original_inode);