BUG: SlicerAbstractCoreModule - Properly delete representations

Representation instances must both be deleted and removed from
the associated representation list.

Co-authored-by: Jean-Christophe Fillion-Robin <jchris.fillionr@kitware.com>

From: Linus Sherrill <linus.sherrill@kitware.com>

git-svn-id: http://svn.slicer.org/Slicer4/trunk@22932 3bd1e089-480b-0410-8dfb-8563597acbee