wasi/io: remove dead files

Author: RalfJung

library/std/src/os/wasi/io/fd.rs

@@ -4,3 +4,7 @@
 
 #[stable(feature = "io_safety_wasi", since = "1.65.0")]
 pub use crate::os::fd::*;
+
+// Tests for this module
+#[cfg(test)]
+mod tests;