Bug 14810 Improve messages in patron anonymizing tool

Bug 14810 Improve messages in patron anonymizing tool

To test:
Create circulation records
Go to 'http://localhost:8081/cgi-bin/koha/tools/cleanborrowers.pl'
Anonymize patron checkout history
Message should read 'All checkouts older than [date] have been
 anonymized
When patch is not applied, message reads 'All patrons with checkouts
 older than [date]  have been anonymized"

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit e38564d2132e1e102cec23d239fb81cd987b3de8)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>