Use VTK_USE_TK to enable or disable RenderingTk

This restores earlier behavior of this option.

CMakeLists.txt

@@ -125,6 +125,14 @@ else ()
   list(APPEND vtk_rejected_modules
     VTK::Java)
 endif ()
+# For vtkTkRenderWidget (only useful with Python, since WRAP_TCL is gone)
+if (VTK_USE_TK)
+  set(VTK_GROUP_ENABLE_Tk YES)
+else ()
+  set(_vtk_module_group_default_Tk "DONT_WANT")
+  list(APPEND vtk_rejected_modules
+    VTK::RenderingTk)
+endif ()
 if (VTK_USE_MPI)
   set(VTK_GROUP_ENABLE_MPI ON)
 else ()