Remove image tests for DSF
There isn't currently an `image.dsf`, so those tests fail.
@@ -910,9 +910,8 @@ else:
HAVE_DSF = True
-@unittest.skipIf(not HAVE_DSF, "mutagen < 1.37")
-class DSFTest(ReadWriteTestBase,
- ExtendedImageStructureTestMixin, unittest.TestCase):
+@unittest.skipIf(not HAVE_DSF, "Mutagen does not have DSF support")
+class DSFTest(ReadWriteTestBase, unittest.TestCase):
extension = 'dsf'
audio_properties = {
'length': 0.01,
