Bug 37844: Remove C4::Members::DeleteUnverifiedOpacRegistrations

Bug 37844: Remove C4::Members::DeleteUnverifiedOpacRegistrations

This patch removes the subroutine
C4::Members::DeleteUnverifiedOpacRegistrations and use the
Koha::Objects->filter_by_last_update method that is used for the other
flag in this script.

Test plan:
Confirm that --del-unv-selfreg works the same before and after this
patch applied

Signed-off-by: Sukhmandeep Benipal <sukhmandeep.benipal@inLibro.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>