Remove Box wrap of Cgroup.hire

It's unnecessary.

Signed-off-by: Tim Zhang <tim@hyper.sh>

tests/cpu.rs

@@ -13,8 +13,7 @@ use std::fs;
 #[test]
 fn test_cfs_quota_and_periods() {
     let h = cgroups::hierarchies::auto();
-    let h = Box::new(&*h);
-    let cg = Cgroup::new(h, String::from("test_cfs_quota_and_periods"));
+    let cg = Cgroup::new(&*h, String::from("test_cfs_quota_and_periods"));
 
     let cpu_controller: &CpuController = cg.controller_of().unwrap();