Bug 16966: Koha::Patrons - Move GetBorrowersWithIssuesHistoryOlderThan to search_patr...

Bug 16966: Koha::Patrons - Move GetBorrowersWithIssuesHistoryOlderThan to search_patrons_to_anonymise

The C4::Members::GetBorrowersWithIssuesHistoryOlderThan subroutine is supposed
to return the patrons with an issue history older than a given date.

It would make more sense to return a list of Koha::Patrons.

On the way, the code from AnonymiseIssueHistory will be moved as well to
anonymise_issue_history.

Note that these 2 subroutines are strongly linked: one is used to know the
number of patrons we will anonymise the history, the other one is used to
anonymise the issues history. The problem is that the first one is not used to
do the action, but only for displayed purpose.

In some cases, these 2 values can differ, which could be confusing.
Case 1:
The logged in librarian is not superlibrarian and IndependentBranches is set:
if 2+ patrons from different libraries match the date parameter, the interface
will display "Checkout history for 2 patrons will be anonymized", when actually
only 1 will be.
Case 2:
If 2+ patrons match the date parameter but one of them has his privacy set to
forever (privacy=0), the same issue will appear.

This patch moves the code from C4::Members::GetBorrowersWithIssuesHistoryOlderThan
to Koha::Patrons->search_patrons_to_anonymise and from
C4::Circulation::AnonymiseIssueHistory to
Koha::Patrons->anonymise_issue_history

Test plan:
1/ Confirm the 2 issues and make sure they are fixed using the Batch
patron anonymization tool (tools/cleanborrowers.pl)
2/ At the OPAC, use the 'Immediate deletion' button to delete all your
reading history (regardless the setting of the privacy rule)
3/ Use the cronjob script (misc/cronjobs/batch_anonymise.pl) to
anonymise patrons.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>