staging: lustre: obd: rename obd_unpackmd() to md_unpackmd()

obd_unpackmd() is only implemented by LMV so move it from OBD
operations to OBD MD operations and update the prototype to reflex
the actual usage. Remove the unused function obd_free_memmd().

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5814


Signed-off-by: Jinshan Xiong <jinshan.xiong@intel.com>
Reviewed-on: http://review.whamcloud.com/13737


Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>