Fixed anyOf not validating when banUnknownProperties is true

This should fix #74 and #128. I just removed [this line](https://github.com/geraintluff/tv4/blob/2a32c8c6dccab69a63ed9d9a9fd86f8e036a4136/source/combinations.js#L60) and the previous tests still pass and my quickly cobbled together test failed before and passes after the fix.