Drop dummy test cases

As commit d5ed19b introduced dynamic test case
discovery using `unittest` default mechanisms, creation of dummy test cases
for unavailable is obsolete and therefore removed.

package_control/tests/test_downloaders.py

@@ -143,13 +143,8 @@ class WgetDownloaderTests(unittest.TestCase, DownloaderTestsMixin):
 if hasattr(downloaders, 'OscryptoDownloader'):
     class OscryptoDownloaderTests(unittest.TestCase, DownloaderTestsMixin):
         downloader_class = downloaders.OscryptoDownloader
-else:
-    class OscryptoDownloaderTests(unittest.TestCase):
-        pass
+
 
 if hasattr(downloaders, 'WinINetDownloader'):
     class WinINetDownloaderTests(unittest.TestCase, DownloaderTestsMixin):
         downloader_class = downloaders.WinINetDownloader
-else:
-    class WinINetDownloaderTests(unittest.TestCase):
-        pass