Avoid DeprecationWarning in unit test.

No need to check for every invalid type that can be used in indexing.

Author: pavoljuhas

diffpy/Structure/tests/TestStructure.py

@@ -271,7 +271,6 @@ def test___getitem__(self):
         self.assertTrue(stru[1] is stru['B'])
         stru[1].label = 'A'
         self.assertRaises(IndexError, stru.__getitem__, 'A')
-        self.assertRaises(IndexError, stru.__getitem__, stru[0])
         return