ext: Remove dead code from fixture.py

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

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

Change-Id: Ifa55a846ba22a84a0f684ffbf870506af7c1045c
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/30238
Maintainer: Bobby R. Bruce <bbruce@ucdavis.edu>
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Hoa Nguyen <hoanguyen@ucdavis.edu>

ext/testlib/fixture.py

@@ -26,17 +26,10 @@
 #
 # Authors: Sean Wilson
 
-import copy
-import traceback
-
 import testlib.helper as helper
-import testlib.log as log
 
 class SkipException(Exception):
     def __init__(self, fixture, testitem):
-        self.fixture = fixture
-        self.testitem = testitem
-
         self.msg = 'Fixture "%s" raised SkipException for "%s".' % (
                fixture.name, testitem.name
         )
@@ -74,22 +67,12 @@ class Fixture(object):
     def skip(self, testitem):
         raise SkipException(self.name, testitem.metadata)
 
-    def init(self, *args, **kwargs):
-        pass
-
     def setup(self, testitem):
         pass
 
     def teardown(self, testitem):
         pass
 
-    def skip_cleanup(self):
-        '''
-        If this method is called, then we should make sure that nothing is
-        done when the teardown() function is called.
-        '''
-        pass
-
     def set_global(self):
         self._is_global = True