Bug 31776: Fix a typo in cleanup_database.pl cronjob's help/usage

Bug 31776: Fix a typo in cleanup_database.pl cronjob's help/usage

cleanup_database.pl cronjob has a typo in it's usage/help:
"preserve-logs" option should be "preserve-log" as it is everywhere
in the code.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
(cherry picked from commit b04e8185a3e76004b152b877d7109f6534ef7371)

Signed-off-by: Lucas Gass <lucas@bywatersolutions.com>
(cherry picked from commit dee700810e56bbf6521c72c42ae5b959267c0f53)
Signed-off-by: Arthur Suzuki <arthur.suzuki@biblibre.com>