python: Replace orderdict with collections.OrderedDict

Python 2.7 and newer has support for ordered dictionaries in the
standard library. Remove this custom class.

Change-Id: I4b720405aa3c4ce8d5c0b401eefe744a85ac3a3e
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/16362
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>

src/python/m5/util/__init__.py

@@ -51,7 +51,6 @@ import jobfile
 from attrdict import attrdict, multiattrdict, optiondict
 from code_formatter import code_formatter
 from multidict import multidict
-from orderdict import orderdict
 from smartdict import SmartDict
 from sorteddict import SortedDict