LU-14838 osc: Remove client contention support

LU-14838 osc: Remove client contention support

Lockless buffered i/o and contention detection don't work,
lockless bufferd i/o is unfixable and contention detection
is broken enough that it will have to be rewritten.

Let's remove both.  This patch starts the removal by
pulling the client side support.

Lustre-change: https://review.whamcloud.com/44205
Lustre-commit: 5ad00e36eca11a1469588bd7b7b4d8df1c32eb27

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: If8583eff176bddb33e197befb967d229f8ca5688
Reviewed-on: https://review.whamcloud.com/44437
Reviewed-by: Bobi Jam <bobijam@hotmail.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>