fix clippy warnings

src/uu/login/src/login.rs

@@ -4,10 +4,7 @@
 // file that was distributed with this source code.
 
 use clap::crate_version;
-use clap::{Arg, Command};
-use std::process::{Command as SystemCommand, Stdio};
-use std::thread::sleep;
-use std::time::Duration;
+use clap::Command;
 use uucore::{error::UResult, format_usage, help_about, help_usage};
 
 const ABOUT: &str = help_about!("login.md");
@@ -15,7 +12,7 @@ const USAGE: &str = help_usage!("login.md");
 
 #[uucore::main]
 pub fn uumain(args: impl uucore::Args) -> UResult<()> {
-    let matches = uu_app().try_get_matches_from(args)?;
+    let _matches = uu_app().try_get_matches_from(args)?;
     Ok(())
 }