E3DObjList is not needed, remove. Remove memeber from
E3DObject, derive E3DScene directly from SdrObjList, some
cleanups in SdrObject, too

Change-Id: Ifa4620a800c14faf21f8b80fd4dc1d39f71be804
Reviewed-on: https://gerrit.libreoffice.org/52740Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Armin Le Grand <Armin.Le.Grand@cib.de>