systemc: Stop using python to set/manage the global time resolution.

systemc: Stop using python to set/manage the global time resolution.

Now that that's managed in c++, we can do that directly without having
to depend on the python code being available, the code which lets us
call from c++ to python, or for the embedded python interpretter to
have started running and have loaded the appropriate modules.

Change-Id: Ied110d8f22181095f8c0c645636a9bd67964263e
Reviewed-on: https://gem5-review.googlesource.com/c/14056
Maintainer: Gabe Black <gabeblack@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>