LU-11939 tgt: Do not assert during grant cleanup

LU-11939 tgt: Do not assert during grant cleanup

Client/server grant inconsistencies discovered during
cleanup are indicative of a bug, but any problems they
would cause have already occurred at this point.

So do not assert during this cleanup.

Signed-off-by: Patrick Farrell <pfarrell@whamcloud.com>
Change-Id: Ic9b827b1005bc321a290505a368349699ddf2f38
Reviewed-on: https://review.whamcloud.com/34215
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Alex Zhuravlev <bzzz@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>