Don't copy *Python.so files during installation.
Copying the VTK's Python C++ module files during install (instead of
install as targets) causes issues like paraview/paraview#17835 (closed).
Fixed vtk_python_package
to no install vtk.*Python.[so|pyd]
files.
Install rules added in vtkPythonWrapping.cmake
already take care of
installing those targets using install(TARGETS..)
call.