Hi Bob,
you can remove them one by one from the bookmarks bar manually, via the bookmarks manager or all at once by deleting the "Bookmarks" file located in "c:\Users\<YourUserName>\AppData\Local\AVAST Software\Browser\User Data\Default" folder. If you are to delete the file, you may want to make a copy beforehand.
Also, one tests comes to my mind now. If you add an extra bookmark to Chrome, which is not present in your Avast browser, will it be imported in our browser when you initiate a new import?
Thank you!
Pavel @ Avast