simplified ratrig v-core 3/3.1 rear XY idler

thingiverse

### The Why After assembling my own v-core 3, I just found out that the RatRig engineers at least at first iterations designed their parts in a bit not optimized for 3d printing way. I personally already break one stepper motor because of these idler's designs and had to change all of the idlers on the printer's rear ### The What So designed simplified idlers and already using them for almost a year now I can confirm that this part is well tested, easy to print, and easy to track visually the status of pulleys and belts on the rear. The left idler mount consists of two parts so a support 625zz bearing have to be added. Will appreciate comments and critics of my design. Cheers :)