Merge pull request #165 from utam0k/fix-cgroup-v2-remove-dir

Use `remove_dir` instead of `remove_dir_all` because youki doesn't have permission to delete contents in cgroup directory.

src/cgroups/v2/manager.rs

@@ -142,7 +142,7 @@ impl CgroupManager for Manager {
 
     fn remove(&self) -> Result<()> {
         log::debug!("remove cgroup {:?}", self.full_path);
-        fs::remove_dir_all(&self.full_path)?;
+        fs::remove_dir(&self.full_path)?;
 
         Ok(())
     }