Remove unnecessary class from helpers.file_utils

A class which keeps track of temporary files and removes them
automatically when they're not needed anymore might be a good idea,
but this implementation didn't remove files in some cases. Adding
unrelated methods that could as well be just standalone functions
is bad design, too.

In this case, it's better to just get rid of it altogether instead
of fixing it, since Python 3 has a TemporaryDirectory class, which
can be used for the same purpose and is definitely more
battle-tested.

tests/sync_app_functional_test_base.py

@@ -5,7 +5,6 @@ from webtest import TestApp
 
 from ankisyncd.users import SqliteUserManager
 from helpers.collection_utils import CollectionUtils
-from helpers.file_utils import FileUtils
 from helpers.mock_servers import MockRemoteServer
 from helpers.monkey_patches import monkeypatch_db, unpatch_db
 from helpers.server_utils import ServerUtils
@@ -15,15 +14,11 @@ class SyncAppFunctionalTestBase(unittest.TestCase):
 
     @classmethod
     def setUpClass(cls):
-        cls.fileutils = FileUtils()
         cls.colutils = CollectionUtils()
         cls.serverutils = ServerUtils()
 
     @classmethod
     def tearDownClass(cls):
-        cls.fileutils.clean_up()
-        cls.fileutils = None
-
         cls.colutils.clean_up()
         cls.colutils = None