The 1st Amendment cuts both ways there - you can't be punished for removing something from your billboard. That's your freedom as a US entity to decide what you express. The reasoning behind why you removed content (a violation of your website's terms, a request from a foreign government, contractual obligation with McDonalds to not host Pink Slime videos in exchange for $1MM a year) doesn't matter from a constitutional perspective. So the US government revoking a protection of an existing US law as punishment for an expression (removing content) would be an unconstitutional violation of free expression.