Bug 16850: Remove C4::Members::IsMemberBlocked

Bug 16850: Remove C4::Members::IsMemberBlocked

This subroutine is only called once and can be replaced with a call to
is_debarred and has_overdues.
Note that prior to this patch, IsMemberBlocked copy/paste code from
HasOverdues, which did not make sense.

Test plan:
Debar a patron and make sure he is not able to checkout (the librarian
is asked to overwrite if OverduesBlockCirc is set to 'confirmation')
Remove the debarment and add overdues to this patron, same as
previously, the checkout should be blocked

Signed-off-by: Owen Leonard <oleonard@myacpl.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>