Add option to use countersunk M4 screws instead of steel plates

[fiferboy]

This is more of a proof-of-concept than anything, but I was finding it difficult to create the custom steel plates for the bearings to ride on in TapChanger-lite. I hit upon the idea of using flat head countersunk hardware to provide a surface for the bearings that allows adjustment and is easier for the average person to obtain.

It remains to be seen if this is a stable alternative, but it is an easy print and just requires 4 M4x8mm countersunk flat head screws to test out. I also used 2 M3x8mm countersunk screws for the upper bearings while I was at it, but that isn't required to test this mod.

Changes include:

• remove the pockets for steel plates in the Stealthburner mount
• add holes for M4 countersunk screws for the bearings to ride on
• even though these screws aren't part of the Voron BOM they are still easy to obtain and don't require precise custom cutting
• using the countersunk screws gives 6 areas for fine adjustment to get the bearings riding nicely without binding while still providing a solid fit with minimal play