This commit reverts r24723 (BUG: Workaround MRML Scene import
limitation. Fixes #3462, #2849 and #4080).

It turns out that this commit had unintended side effects. The following
tests were failing:

 py_LandmarkRegistration
 py_SlicerMRBMultipleSaveRestoreTest
 py_SlicerMRBMultipleSaveRestoreLoopTest
 py_SlicerMRBTest
 py_NeurosurgicalPlanningTutorialMarkupsSelfTest
 qMRMLSceneModelTest

After concerting with the core team, since the correct fix involves
changes in the core of MRML, we decided to revert this commit and mark
the tickets #3462, #2849, #4080 as known issues in the release note.

git-svn-id: http://svn.slicer.org/Slicer4/trunk@24734 3bd1e089-480b-0410-8dfb-8563597acbee