COMP: Simplify MRML Scene API removing "Edited()" method. Fixes #3472

For sake of consistency, remove Edited method. Indeed, this was the only
event triggered using this approach and it was not observed. For reference,
this method was first introduced by commit r7727.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@23152 3bd1e089-480b-0410-8dfb-8563597acbee