Remove knockoutjs_classBindingProvider example

Fixes #721

KnockoutJS is very versatile and can be integrated with almost every framework
or combined with a wide range of supporting library.
TodoMVC, however, is not a good place to explore or all possible permutations of
frameworks and libraries and tries to focus on widely used combinations.

@sindresorhus Can you check if I didn't miss anything? We can then link to this PR in the wiki.