staging/lustre/lustre_user.h: remove obsolete comments

This is only part of the original Lustre commit, main part of which changes
user space code. And now the comments above struct hsm_copy is no more true.

Lustre-change: http://review.whamcloud.com/4737
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-2062


Signed-off-by: JC Lafoucriere <jacques-charles.lafoucriere@cea.fr>
Signed-off-by: Henri Doreau <henri.doreau@cea.fr>
Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Peng Tao <bergwolf@gmail.com>
Signed-off-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>