[Sofa/tests] Remove the invalid tests/Core/PythonRestShapeForceField.py

The code in binding/Sofa/tests/Core/PythonRestShapeForceField.py seems outdated and not used anymore for testings.
A fully working example is in examples/PythonRestShapeForceField.py

So let's remove the one that is broken and not used.

Author: damienmarchal