LU-9679 osc: remove cl_io_cancel()

LU-9679 osc: remove cl_io_cancel()

cl_io_cancel() is never used, so remove it and various
other things that it is the only user of.

Signed-off-by: Mr NeilBrown <neilb@suse.com>
Change-Id: I6cf9b53aa7fc3379e57fa0ac0ea236ccda4ff6b7
Reviewed-on: https://review.whamcloud.com/37597
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>