Remove an overly specific exception message test.

Lib/test/test_import.py

@@ -283,8 +283,6 @@ class ImportTests(unittest.TestCase):
             self.skipTest('path is not encodable to {}'.format(encoding))
         with self.assertRaises(ImportError) as c:
             __import__(path)
-        self.assertEqual("Import by filename is not supported.",
-                         c.exception.args[0])
 
     def test_import_in_del_does_not_crash(self):
         # Issue 4236