Simplified temporary directory handling in AdminScriptTestCase.

Use tempfile.TemporaryDirectory() in AdminScriptTestCase.setUp()
to create and destroy a temporary directory for each test. It removes
the need for individual tests to delete files.

For test classes that don't use the temporary directory, inherit from
SimpleTestCase.

tests/logging_tests/tests.py

@@ -439,6 +439,7 @@ class SettingsConfigTest(AdminScriptTestCase):
     a circular import error.
     """
     def setUp(self):
+        super().setUp()
         log_config = """{
     'version': 1,
     'handlers': {
@@ -450,9 +451,6 @@ class SettingsConfigTest(AdminScriptTestCase):
 }"""
         self.write_settings('settings.py', sdict={'LOGGING': log_config})
 
-    def tearDown(self):
-        self.remove_settings('settings.py')
-
     def test_circular_dependency(self):
         # validate is just an example command to trigger settings configuration
         out, err = self.run_manage(['check'])
@@ -518,6 +516,7 @@ class SettingsCustomLoggingTest(AdminScriptTestCase):
     callable in LOGGING_CONFIG (i.e., logging.config.fileConfig).
     """
     def setUp(self):
+        super().setUp()
         logging_conf = """
 [loggers]
 keys=root
@@ -544,7 +543,6 @@ format=%(message)s
 
     def tearDown(self):
         self.temp_file.close()
-        self.remove_settings('settings.py')
 
     def test_custom_logging(self):
         out, err = self.run_manage(['check'])