usb_hub: do not explicitly import AsRef which is part of prelude

AsRef is always available, no need to import it.
This was suggested by cargo clippy.

Signed-off-by: Leonard Göhrs <[email protected]>

Author: hnez

src/usb_hub.rs

@@ -31,7 +31,6 @@ use crate::watched_tasks::WatchedTasksBuilder;
 #[cfg(feature = "demo_mode")]
 mod rw {
     use std::collections::HashMap;
-    use std::convert::AsRef;
     use std::io::Result;
     use std::path::Path;
     use std::sync::Mutex;