LU-8191 target: convert functions to static

LU-8191 target: convert functions to static

Static analysis shows that a number of functions
could be made static. This patch declares several
functions in target static.

Also, remove an unused function tgt_obd_log_cancel(),
and add some headers where they were missing.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: I1823df3562cb181b275788560166c92b63483637
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51475
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: jsimmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>