hm,
All those marks are Locked, so they must be Unlocked before you attempt to delete them.
Use Command-A to select everything on the page. Then, Arrange > Unlock will unlock everything.
Now you are free to click on things and then hit the Delete key to make them disappear. If you make a mistake, COMMAND-Z to restore the last deleted item.
You might not be aware, and it may not matter, but there is a large white rectangle behind the text and in front of the black lines that is used to mask off the lines evenly. That's its only function as far as I can determine, so I think you could delete that too.
Hope this helps.
Jerry