Remove deprecated endpoint: account/update_delivery_device

Relevant output from the tests:

```python
======================================================================
ERROR: testsetdeliverydevice (__main__.TweepyAPITests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests.py", line 153, in test_set_delivery_device
    self.api.set_delivery_device('im')
  File "/home/dialelo/repos/tweepy/tweepy/binder.py", line 185, in _call
    return method.execute()
  File "/home/dialelo/repos/tweepy/tweepy/binder.py", line 168, in execute
    raise TweepError(error_msg, resp)
TweepError: [{u'message': u'This endpoint is deprecated and should no longer be used', u'code': 68}]

```