LU-17704 revert: "LU-17379 ptlrpc: fix check for callback discard"

LU-17704 revert: "LU-17379 ptlrpc: fix check for callback discard"

This reverts commit a6886dba0ed8a622c9831cd33d310d933492c72d.
This is failing dbench intermittently in sanity-benchmark.

Change-Id: Id3720c79ca8dd9276e086aab5d3fcfe43ddd680a
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54686
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Yang Sheng <ys@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Stephane Thiell <sthiell@stanford.edu>