Finite funds and finite space necessitate that libraries weed their collections. And when they do, they indicate which books they are removing by a variety of stamps or handwritten words, like this one:
But this one?
Obsolete? Well, some books are indeed obsolete. Books that talk about the Soviet Union as if it still exists, for example. Atlases that show Czechoslovakia. Books that have scientific information that has since been proved incorrect, or for which new terminology has been agreed upon (e.g. Is Pluto a planet?)
But this was a picture book. A picture book about a child who is visited by a king and his royal entourage... which turns out to have all been in the child's imagination, piqued by a deck of playing cards. This book is not, and could never be, obsolete.