smtk: use a relative path

CMake does the install prefix logic automatically.

Projects/smtk.cmake

@@ -9,7 +9,7 @@ if (WIN32)
   # in a different place than Unix builds and in a different
   # place than SMTK would put it by default. Tell SMTK where
   # to install Python source for the smtk module:
-  list(APPEND extra_cmake_args "-DSMTK_PYTHON_MODULEDIR:PATH=${SuperBuild_BINARY_DIR}/install/python")
+  list(APPEND extra_cmake_args "-DSMTK_PYTHON_MODULEDIR:PATH=python")
 endif()
 
 set(smtk_libdir lib)