Issue #20617: Remove unused import in test_ssl.

Patch by Mark Lawrence.
diff --git a/Lib/test/test_ssl.py b/Lib/test/test_ssl.py
index 779b622..99a317a 100644
--- a/Lib/test/test_ssl.py
+++ b/Lib/test/test_ssl.py
@@ -18,7 +18,6 @@
 import weakref
 import platform
 import functools
-from unittest import mock
 
 ssl = support.import_module("ssl")