Is there a way to erase the +, - buttons and compass image?

To disable the compass, you can add &nocompass=true to the Dynmap URL (make sure to put this before the pound symbol!). To disable the zoom buttons is a little harder and there doesn't seem to be a built-in way to do it, but you can probably change line 178 (or whatever line specifies zoomControl) of the file web/js/map.js to zoomControl: false,. You can also disable everything (including the sidebar) by add &nogui=true to the URL query parameters.