remove __cmp__ methods in client.dynamic

[junkmd]

THIS IS FOR drop_py2 PLAN! Please see #392.

In Python3,

The cmp() function should be treated as gone, and the cmp() special method is no longer supported.
https://docs.python.org/3/whatsnew/3.0.html#ordering-comparisons

However, they are still contained in client.dynamic.

comtypes/comtypes/client/dynamic.py

Lines 76 to 79 in 32d6621

	def __cmp__(self, other):
	if not isinstance(other, _Dispatch):
	return 1
	return cmp(self._comobj, other._comobj)

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.