It says that their license to display the image is subject to your privacy settings. Simply setting the image to Only You doesn't remove the image, but would ensure no one can see it. It effectively revokes Facebook's license to show the image to all your friends. If none of your friends can view it, they cannot share it, and it should remove any of their previous shares. Then you can delete it.
EDIT: Come to think of it, I have a feeling that "unless your content has been shared with others" behaves more narrowly in practice than it could by reading the text. Probably, it would apply to edges cases beyond Facebook's reasonable control - like a notification of a picture to a phone. The app only checks for updates every so often, and it may be out of service for a while, but a thumbnail is sent. You could delete the image, but until they check Facebook's servers, the person has effective control over the thumbnail, which is a derivative work of your copyrighted image, legally. Facebook is just covering their bases there.
But wait. What if another person's privacy settings preclude one's ability to know if people have shared my content or not, and/or whether those people deleted it?
Doesn't that place Facebook in a realm of ultimate deniability with respect to whether or not they are still in lawful possession of this implicit IP License?
Case in point:
So when you "share with others" (whatever that might specifically mean, according to how they've defined their user interface at that particular moment), that very action is potentially bestowing onto Facebook potentially eternal IP rights to distribute that content forever.Like, simply by virtue of sharing, any person who then accesses the content and then re-shares it and refuses to delete it, is then acting as the de-facto rights holder from which all of Facebook's privileges are derived.
But by letting another Facebook user access your shared content, as a peer, it's not immediately clear where that peer truly derives their eternal permission to forever re-share everything they ever had access to as your friend. Why does that person possess eternal rights to share YOUR content on Facebook, simply by being listed as your friend? Where does that part come from? Isn't that behavior enabled by Facebook? And doesn't Facebook reserve the right to redefine how things are "shared" at will? So then, doesn't that mean that Facebook is enabling itself?
Doesn't it seem like there is strong potential for a conflict of interest between Facebook and the other two parties involved?