Prusa i3 MK2 Y Chassis Bearing Straps

Mostly cosmetic changes to http://www.thingiverse.com/thing:1819779 which didn't render cleanly, due to faces, added and removed such that they evaluate to the same plane. Consequently, renderers weren't quite decided whether to add or remove the faces, and showed them as artefacts. Also removed a positioning error, but refrained from doing a much needed simplification of this thing.