Bug 19008: More database cleanups - statistics

Bug 19008: More database cleanups - statistics

misc/cronjobs/cleanup_database.pl provides some database cleanup.
Yet some tables that could need cleanup are not in this script.

This patch adds cleanup for statistics table.

Test plan :
- Count statistics : select count(*),date(datetime) from statistics group by date(datetime);
- Run cleanup : misc/cronjobs/cleanup_database.pl -v --statistics 30
- Recount statistics

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>