LU-17848 osd: dt_tunables_fini() and friends return void

LU-17848 osd: dt_tunables_fini() and friends return void

The function dt_tunables_fini() can't really fail. Make
it return void. Make the various osd_procfs_fini()
implementations also return void.

Test-Parameters: trivial
Test-Parameters: trivial fstype=zfs
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I5edc7ed43fad69d6ebdd734d8e9fdc69cdcf0915
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/59418
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Lijing Chen <lijinc@amazon.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>