Improve the warning message for invalid escape sequences

Lib/test/test_unicode.py

 """ Test script for the Unicode implementation.
 
 Written by Marc-Andre Lemburg (mal@lemburg.com).
 
 (c) Copyright CNRI, All Rights Reserved. NO WARRANTY.
 
 """
 import _string
 import codecs
 import itertools
@@ skipping 2395 matching lines @@
         self.assertTrue(astral < astral2)
         self.assertTrue(astral >= ascii)
         self.assertTrue(astral >= latin)
         self.assertTrue(astral >= bmp2)
         self.assertFalse(astral >= astral2)
 
     def test_free_after_iterating(self):
         support.check_free_after_iterating(self, iter, str)
         support.check_free_after_iterating(self, reversed, str)
 
-    def test_invalid_sequences(self):
-        for letter in string.ascii_letters + "89": # 0-7 are octal escapes
-            if letter in "abfnrtuvxNU":
-                continue
-            with self.assertWarns(DeprecationWarning):
-                eval(r"'\%s'" % letter)
-
 
 class CAPITest(unittest.TestCase):
 
     # Test PyUnicode_FromFormat()
     def test_from_format(self):
         support.import_module('ctypes')
         from ctypes import (
             pythonapi, py_object, sizeof,
             c_int, c_long, c_longlong, c_ssize_t,
             c_uint, c_ulong, c_ulonglong, c_size_t, c_void_p)
@@ skipping 436 matching lines @@
             "obj",
             [(True, 'arg'),
              (False, 'key1'),
              (False, 'key2'),
             ]])
         self.assertRaises(TypeError, _string.formatter_field_name_split, 1)
 
 
 if __name__ == "__main__":
     unittest.main()