LU-2489 hsm: remove hsm_nl proc file

LU-2489 hsm: remove hsm_nl proc file

Remove the file /proc/fs/lustre/mdc/*/hsm_nl which was introduced "for
testing purposes."

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I646c74de00084a54d528b059633512381e7097f0
Reviewed-on: http://review.whamcloud.com/6656
Tested-by: Hudson
Reviewed-by: jacques-Charles Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Reviewed-by: Aurelien Degremont <aurelien.degremont@cea.fr>
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>