Remove Python2 generator work around

[wd60622]

Seems stale:

pymc/pymc/data.py

Lines 111 to 121 in b36e573

	def __next__(self):
	"""Next value in the generator."""
	if not self._yielded_test_value:
	self._yielded_test_value = True
	return self.test_value
	else:
	return smarttypeX(copy(next(self.gen)))
	# python2 generator
	next = __next__

[ricardoV94]

That whole thing is deprecated (if you trigger it via the user-facing API)

[wd60622]

I see the deprecation warning dating to August. Can I do the honors of removing?

[ricardoV94]

Sure