Now that kconfigfunctions.py is loading the EDT object from a pickle
file, I can't find any other reads of the environment variables it was
previously using to do that.
(The CMake variables with the same names are read in different places;
I'm specifically talking about environment variables here.)
Remove the dead stores.
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>
