bpo-29919: Remove unused imports found by pyflakes (#137)

Make also minor PEP8 coding style fixes on modified imports.
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 416316c..d2420e9 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -18,7 +18,7 @@
 import unittest
 import warnings
 from operator import neg
-from test.support import TESTFN, unlink,  run_unittest, check_warnings
+from test.support import TESTFN, unlink, check_warnings
 from test.support.script_helper import assert_python_ok
 try:
     import pty, signal