Yahoo CAN remove any website from its rankings for any reason or no reason. Google was just vindicated in a lawsuit where a company sued them for ranking other sites above his (and the ironic loss of AdSense revenue that ensued) by a Judge who ruled that SERPs are a form of 1st Amendment protected speech.
Its kind of like a restaurant reviewer. If he says my restaurant is better than yours, he has the right to say that and you can't legally do anything about it, unless what he says is slanderous.
Now WOULD Yahoo drop a site that has AdSense? That would be interesting. Think about all of the people who have AdWords campaigns that direct low cost clicks to AdSense cluttered landing pages. These landing pages are little more than online spam typically. So the question then becomes WOULD Yahoo rank spam sites over content-rich sites?
I doubt they knocked you or anyone else because of AdSense, but if you had a landing page with little content and
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