Bug 15398: Hide Staff members only in the patron deletion/anonymization tool

Bug 15398: Hide Staff members only in the patron deletion/anonymization tool

On bug 9076 (commit 568a4c1230ee9a4002181fcab2c083faf6c323a9), the plan
was to hide the Staff members from the tool.
But the test was wrong, it was done on the category_code instead of the
category_type value.

Test plan:
1/ Create a category 'Student' which is not part of the Staff
(category_code=S, category_type!=S)
2/ Create a staff category (category_type=S)
3/ Go on the deletion/anonymization tool (tools/cleanborrowers.pl) and
confirm that the category Student category is displayed in the dropdown
list.

Signed-off-by: Bernardo Gonzalez Kriegel <bgkriegel@gmail.com>
Work as described, no errors.

Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
http://bugs.koha-community.org/show_bug.cgi?id=15308

Signed-off-by: Brendan A Gallagher <brendan@bywatersolutions.com>
(cherry picked from commit 6f0cdee69b670f1c49693198e335deb26470d961)
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>