Lioncash a7d9fe993a service/fsp_srv: Implement CleanDirectoryRecursively
This is the same behavior-wise as DeleteDirectoryRecursively, with the
only difference being that it doesn't delete the top level directory in
the hierarchy, so given:

root_dir/
  - some_dir/
    - File.txt
  - OtherFile.txt

The end result is just:

root_dir/
2018-11-30 20:17:28 -05:00
..
2018-10-02 15:30:48 +02:00