In Consul 1.15.0, the Delete Token API was changed so as to return an error when
deleting a non-existent ACL token. This means that if Nomad successfully deletes
the token but fails to persist that fact, it will get stuck trying to delete a
non-existent token forever.
Update the token deletion function to ignore "not found" errors and treat them
as successful deletions.
Fixes: #17833
Tim Gross