We do NOT advise deleting any content that you know you will not use. Instead, please make a page private in order to hide the content you do not want your students to see. You can make a page private by:
1. Going into the Organize view of your book.
2. Find the page you want to hide from students.
3. Uncheck the Show in Web setting checkbox for your selected page.
4. This page will now be hidden from students and non-logged in visitors. However, book editors will still see this page as part of the book and table of content. You can also move it to a new Part at the end of the book, made for housing the items you know you will not need. That way, you can return to it later to mine ideas or content, should the need arise.