LU-10899 obdclass: remove unused ll_import_cachep

LU-10899 obdclass: remove unused ll_import_cachep

The ll_import_cache is not used anywhere, and can be removed.

Test-Parameters: trivial
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I3f43c81ffbf1385117f9ba1f8f9881388a3ebbe5
Reviewed-on: https://review.whamcloud.com/33119
Tested-by: Jenkins
Reviewed-by: John L. Hammond <jhammond@whamcloud.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>