Let me explain. Your document is a presentation document. All presentation documents have a navigation bar embedded that contains a menu with links to all your pages. It pops-up from the left bottom side of the page when you hover mouse over it. It is done with that code you don't like. When you do a single page preview, navigation menu is not exported because it is supposed that you only want to preview the design of the current page, not to navigate throughout entire website (which you wouldn't be able to do anyway since no other pages are exported, unless you have exported them before).
If you don't want this navigation menu to be included with your website, change the document type to Web Document.
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