ext: Remove dead code from configuration.py

This has been tested with vulture:
https://pypi.org/project/vulture

JIRA: https://gem5.atlassian.net/projects/GEM5/issues/GEM5-533

Change-Id: Ibaf812ace94c2ae0e2115552a87fb506a427bb89
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30242
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>

ext/testlib/configuration.py

@@ -84,7 +84,6 @@ import os
 import re
 
 from six import add_metaclass
-from six.moves import configparser as ConfigParser
 from pickle import HIGHEST_PROTOCOL as highest_pickle_protocol
 
 from testlib.helper import absdirpath, AttrDict, FrozenAttrDict
@@ -132,11 +131,6 @@ class _Config(object):
         self._run_post_processors()
         self._initialized = True
 
-    def _init_with_dicts(self, config, defaults):
-        self._config = config
-        self._defaults = defaults
-        self._initialized = True
-
     def _add_post_processor(self, attr, post_processor):
         '''
         :param attr: Attribute to pass to and recieve from the
@@ -220,7 +214,6 @@ def define_defaults(defaults):
                                                       os.pardir,
                                                       os.pardir))
     defaults.result_path = os.path.join(os.getcwd(), '.testing-results')
-    defaults.list_only_failed = False
     defaults.resource_url = 'http://dist.gem5.org/dist/develop'
 
 def define_constants(constants):