The table of contents is created automatically by default for all export types. For EPUB and webbook outputs, the table of contents is necessary in order for users to navigate your book digitally.
However, you can disable the table of contents for your PDF file by going to Appearance Theme Options from the left sidebar menu of your book's dashboard, then selecting the PDF Options tab. Scroll down to the Table of Contents setting. The "Display table of contents" box can be unchecked if you would like to hide the table of contents page in your PDF files.
Be sure to save your changes.