Canada Post Lettermail Measuring Slot for 220mm bed

Modified the existing design created by @SteveHanov to fit on a 220mm x 220mm by rounding the outline. The required postal dimensions were retained, so the model still works. but some of the extra material was removed.

The model needs to be printed at a 45° angle (corner to corner) to fit on the bed. This model has been printed on an Ender 3v2, and should fit any 220mm or larger bed.