Remove old-style classes from `test_cmath`

[sobolevn]

Right now old-style classes are long gone. But, test_cmath still tests for them and has an outdated comment about them being not fully supported:

cpython/Lib/test/test_cmath.py

Lines 258 to 265 in 365852a

	# TypeError should be raised for classes not providing
	# either __complex__ or __float__, even if they provide
	# __int__ or __index__. An old-style class
	# currently raises AttributeError instead of a TypeError;
	# this could be considered a bug.
	self.assertRaises(TypeError, f, NeitherComplexNorFloat())
	self.assertRaises(TypeError, f, MyInt())
	self.assertRaises(Exception, f, NeitherComplexNorFloatOS())

I will send a PR with removal of old style classes, correct exception handling, and comment rewording.

[mdickinson]

Closed in #98728. Thank you for the fix!