Fix dip in front surface of canopy frame

There was some rolloff in some regions of the front edge of the canopy frame which might affect the sealing performance. Up to and including painting the frame I did not notice these variation. However I did notice these when it came to trimming the canopy bubble to match the frame. At the very least there would be some overhang of the canopy bubble material - since I cut this material along a well defined straight edge rather than follow all the variations of the canopy frame which by this stage had been noticed. Such overhang would not be a big deal, but it would be noticeable.

So I decided to grind back the paint and primer, and build up the most serious dips.