LU-16518 lu: remove unused functions in lu_object.h

LU-16518 lu: remove unused functions in lu_object.h

Remove lu_object_ops() and lu_object_assert_not_exists()
since they have no callers. Replace lu_object_assert_exists()
with lu_object_exists(), since it's just a thin wrapper.

Fixes: d2d56f38da01 ("- make HEAD from b_post_cmd3")
Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I74136a0c5283beaf77fdbc6df19387209e1c03f4
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58414
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Mikhail Pershin <mpershin@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>