When you start typing in the address bar, Chrome will automatically suggest sites from your history based on your query. For example, you start typing "g" and the address bar will have "google.com" and other 5 URLs from your bookmarks and history.
A simple way to delete these drop down suggestions is to press Shift + Delete key, while highlighting the URL.
Note that this method will not delete the bookmark suggestion. You will have to first remove the bookmark and them delete from shift+delete key combination. Apart from this method, you should also disable auto suggestions from Chrome settings > Advance > "Use a prediction service to help complete searches and URLs typed in address bar or the App launcher search box".
That's all. The auto suggested site will be permanently deleted and will never return (unless you bookmark them again).
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