Bug 19599: Speed anonymise_issue_history up

Bug 19599: Speed anonymise_issue_history up

The query generated by anonymise_issue_history is unecessary complex and
can be very slow on large DB.
With this patch we will execute one query per patron instead.

See patch "Bug 19599: Simplify the query" on the bug report for an
alternative.

Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit 5be4704347610d269e7d3401f50af46b3202869a)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>