Undefined names in TextThought.delete_surroundings()

[takluyver]

Pyflakes points out that this method refers to variables old and local_bytes which are never defined. It's not clear what they should be, although perhaps old should be orig (which is defined).

These were already missing when TextThought was refactored 4 years ago (185c2c4). I think this method is only called when using advanced input methods, like those for entering Chinese, so I don't know how to test it.