Update test_regrtest.py

Remove an unused "import sys".

Author: Anselm Kruis

Lib/test/test_regrtest.py

@@ -824,7 +824,6 @@ def test_crashed(self):
 class TempCwdTestCase(unittest.TestCase):
     @unittest.skipUnless(hasattr(os, "fork"), "test requires os.fork")
     def test_forked_child(self):
-        import sys
         with support.temp_cwd() as cwd:
             pid = os.fork()
             if pid != 0: