python: Remove the m5.config and options.py mechanism.

It appears that there is a mechanism where you could either have a .m5
directory in your home directory, or set an M5_CONFIG environment
variable to some other directory, where you could put an options.py
file. That file would then be passed the options dict which gem5's main
had extracted from its args, which it could modify as it liked.

First, I suspect that this mechanism was basically unknown and was just
a dark corner of gem5 people had forgotten about. Getting rid of it
will help clear out old cruft.

Second, this sort of file reaching in and fiddling with gem5's internal
data structures is dangerous and fragile, and could in almost any case
be replaced with a wrapper script or shell alias.

Change-Id: Ic828716979ea6379f60de796d23281ab075b38ec
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/56387
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Maintainer: Gabe Black <gabe.black@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>

src/python/SConscript

@@ -217,7 +217,6 @@ PySource('gem5.utils', 'gem5/utils/requires.py')
 PySource('', 'importer.py')
 PySource('m5', 'm5/__init__.py')
 PySource('m5', 'm5/SimObject.py')
-PySource('m5', 'm5/config.py')
 PySource('m5', 'm5/core.py')
 PySource('m5', 'm5/debug.py')
 PySource('m5', 'm5/event.py')