Bug 16844: (follow-up of 15656) Remove export of GetMemberRelatives from C4::Members

Bug 16844: (follow-up of 15656) Remove export of GetMemberRelatives from C4::Members

Bug 15656 removed the C4::Members::GetMemberRelatives subroutine but the
module still exports it.

Test plan:
  git grep GetMemberRelatives
should not return any results.

Signed-off-by: Marc Véron <veron@veron.ch>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
(cherry picked from commit 24a32e975c964caa99bc9f8ebe31f7bd53cdd13e)
Signed-off-by: Frédéric Demians <f.demians@tamil.fr>