LU-10855 llog: remove llog_cancel()

LU-10855 llog: remove llog_cancel()

Remove llog_cancel() and replace its sole use with a direct call to
llog_changelog_cancel(). Simplify the prototype of
llog_changelog_cancel() according to its use.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: I32f5adf34ca10b918e5860e03ef0d8028c941697
Reviewed-on: https://review.whamcloud.com/31795
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Mike Pershin <mike.pershin@intel.com>
Reviewed-by: Sebastien Buisson <sbuisson@ddn.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>