LU-10383 hsm: remove struct hsm_thread_data

LU-10383 hsm: remove struct hsm_thread_data

Remove struct hsm_thread_data. Move allocation of the HSM scan data
requests array to mdt_coordinator().

Test-Parameters: trivial testlist=sanity-hsm
Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I12075dc000c312d2432c8e32787ed36560d1ae42
Reviewed-on: https://review.whamcloud.com/31234
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Reviewed-by: Faccini Bruno <bruno.faccini@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>