Tidy up redundant use declarations. (#3333)

This is just a minor code cleanup.

crates/test-programs/wasi-tests/src/bin/nofollow_errors.rs

@@ -1,4 +1,3 @@
-use libc;
 use more_asserts::assert_gt;
 use std::{env, process};
 use wasi_tests::{assert_errno, open_scratch_directory};