Remove a dead import line.

Noticed by Serhly Storchaka.
diff --git a/Lib/test/test_pep352.py b/Lib/test/test_pep352.py
index 98debf0..7c98c46 100644
--- a/Lib/test/test_pep352.py
+++ b/Lib/test/test_pep352.py
@@ -1,7 +1,6 @@
 import unittest
 import builtins
 import warnings
-from test.support import run_unittest
 import os
 from platform import system as platform_system