LU-14702 osc: cleanup comment in osc_object_is_contended

LU-14702 osc: cleanup comment in osc_object_is_contended

ll_file_is_contended() does not exist any more, so the comment
is invalid.

Test-Parameters: trivial
Signed-off-by: Li Xi <lixi@ddn.com>
Change-Id: Ib68e8dc885e6812065c076d36dc61938a30d6980
Reviewed-on: https://review.whamcloud.com/43775
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>