remove sys.version_info bridges in client.dynamic

[junkmd]

THIS IS FOR drop_py2 PLAN! Please see #392.

In Python3,

PEP 3114: the standard next() method has been renamed to __next__().
https://docs.python.org/3/whatsnew/3.0.html#operators-and-special-methods

However, they are still contained in client.dynamic.

comtypes/comtypes/client/dynamic.py

Lines 161 to 175 in b6a4181

	if sys.version_info >= (3, 0):
	def __next__(self):
	item, fetched = self.enum.Next(1)
	if fetched:
	return item
	raise StopIteration
	else:
	def next(self):
	item, fetched = self.enum.Next(1)
	if fetched:
	return item
	raise StopIteration

Remove this dead code and modernize the codebase.

[junkmd]

I created this issue to serve as a "model case" for future good first issue that I will submit.

I will work on this.