Bug 19126: Fix Members.t with IndependentBranches set

Bug 19126: Fix Members.t with IndependentBranches set

If you enabled that pref, Members.t fails with:
t/db_dependent/Members.t .. 63/63 # Looks like you failed 15 tests of 63.

The first one is:
t/db_dependent/Members.t .. 32/63
   Failed test 'Staff patron not deleted from list'
   at t/db_dependent/Members.t line 304.

Bottle neck is GetBorrowersToExpunge. The results of that sub depend on the
state of this preference.
Trivially fixing it here by disabling the pref before the first call.

Test plan:
[1] Do not apply this patch yet. Enable IndependentBranches.
[2] Run Members.t and observe that it fails.
[3] Apply this patch. And run Members.t again. It should pass now.

Signed-off-by: Aleisha Amohia <aleishaamohia@hotmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>