Fix unused extern crates

src/bin/id.rs

@@ -1,6 +1,5 @@
 extern crate arg_parser;
 extern crate extra;
-extern crate syscall;
 extern crate userutils;
 
 use std::borrow::Borrow;

src/bin/passwd.rs

@@ -3,7 +3,6 @@
 extern crate arg_parser;
 extern crate extra;
 extern crate rand;
-extern crate syscall;
 extern crate termion;
 extern crate userutils;
 

src/bin/su.rs

@@ -2,7 +2,6 @@
 
 extern crate arg_parser;
 extern crate extra;
-extern crate syscall;
 extern crate termion;
 extern crate userutils;
 

src/bin/sudo.rs

@@ -1,5 +1,4 @@
 extern crate arg_parser;
-extern crate extra;
 extern crate syscall;
 extern crate termion;
 extern crate userutils;

src/bin/whoami.rs

@@ -2,7 +2,6 @@
 
 extern crate arg_parser;
 extern crate extra;
-extern crate syscall;
 extern crate userutils;
 
 use std::io::{self, Write};