top: move codes to uu_core

Author: Bluemangoo

src/uu/top/src/header.rs

@@ -52,8 +52,8 @@ fn uptime() -> String {
 pub fn get_nusers_systemd() -> uucore::error::UResult<usize> {
     use std::ffi::CStr;
     use std::ptr;
-    use uucore::libc::*;
     use uucore::error::USimpleError;
+    use uucore::libc::*;
 
     unsafe {
         // systemd