Remove incorrect lines (meant for cdecimal) from recently added Decimal tests.

Lib/test/test_decimal.py

@@ -1521,7 +1521,6 @@ class DecimalUsabilityTest(unittest.TestCase):
     def test_nan_to_float(self):
         # Test conversions of decimal NANs to float.
         # See http://bugs.python.org/issue15544
-        Decimal = self.decimal.Decimal
         for s in ('nan', 'nan1234', '-nan', '-nan2468'):
             f = float(Decimal(s))
             self.assertTrue(math.isnan(f))
@@ -1529,7 +1528,6 @@ class DecimalUsabilityTest(unittest.TestCase):
             self.assertEqual(sign, -1.0 if s.startswith('-') else 1.0)
 
     def test_snan_to_float(self):
-        Decimal = self.decimal.Decimal
         for s in ('snan', '-snan', 'snan1357', '-snan1234'):
             d = Decimal(s)
             self.assertRaises(ValueError, float, d)