Revert "nfs: take extra reference to fl->fl_file when running a LOCKU operation"

This reverts commit db2efec0

.

William reported that he was seeing instability with this patch, which
is likely due to the fact that it can cause the kernel to take a new
reference to a filp after the last reference has already been put.

Revert this patch for now, as we'll need to fix this in another way.

Cc: stable@vger.kernel.org
Reported-by: William Dauchy <william@gandi.net>
Signed-off-by: Jeff Layton <jeff.layton@primarydata.com>
Reviewed-by: "J. Bruce Fields" <bfields@fieldses.org>
Tested-by: "J. Bruce Fields" <bfields@fieldses.org>