Bug 11975: (follow-up) simplify construction of params for GetBorrowersToExpunge()

Bug 11975: (follow-up) simplify construction of params for GetBorrowersToExpunge()

This patch consolidates the code for constructing the parameters for
GetBorrowersToExpunge() into a subroutine.  As a side-effect, this
fixes a regression introduced by the main patch where no patrons would
be deleted when filtering by expiration date.

To test:

[1] Follow the test plan in the main patch.

Signed-off-by: Galen Charlton <gmc@esilibrary.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Galen Charlton <gmc@esilibrary.com>