The book section is essentially still there, it is simply mixed together with some other sections, as a combined section made more sense to me:
Sport, Hobbies and Interests
If you are an avid follower of football or F1, like bird watching or keeping tropical fish,
love reading books or writing, photography, cars or classic bikes, model airplanes or anything like that, then this is the section you need.
Combining those sections made sense due to them all essentially being hobbies, but as individual sections, none were getting enough posts to justify taking up space and making the forum longer. All the existing book posts and threads can be found in that section.