You could edit them out using Fred´s WW2Map editor at:
http://www.wargamer.com/Hosted/Chlan.../SP/ww2map.zip
The editor is a little bit user unfriendly, but what you need to do after starting the program is:
1. Go to "Files" and select "Set SHP Directory". Navigate to your games Graphics folder and select any .shp file there and click Open. (Now the program knows where to the graphics files reside)
2. Go to "Files" again and now select "Load Map" and load your map file.
3. Click on the hex that has the unwanted bridge graphic and select "Options" and from there "Inspection mode".
4. In the Inspection Windows make sure Sec3-Sec7 all read " -" and then click on the button labeled "Retain".
5. Now click on the Redraw map icon in the lower right of the editors main window to see if the unwanted bridge graphic dissapears from the hex.
6. If everything looks ok click on "Files" and "Save Map" to save your map.
Now when you open the map with the games regular map editor the bridge graphics should be gone from the map edges.
Ofcourse the easiest thing to do is just to ignore the bridge graphics in the sides of the map. They are after all just a minor cosmetic flaw.