python: Remove SortedDict from python utilities

python: Remove SortedDict from python utilities

The SortedDict isn't actually used. A developer willing to
use a sorted dictionary should resort to the collections.OrderedDict
instead

Change-Id: Ia2cc664eb01e59b197218ccf40ff9c680a410fb2
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/37796
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>
Tested-by: kokoro <noreply+kokoro@google.com>