Add Bourns PEC12R-2x17F-Nxxxx and remove old 2xxx footprints

Following !3284 (merged), add the no-switch variant with the 17.5mm shaft:

This is very similar to the PEC12R-2x17F-Sxxxx, but the body is 1mm less deep and the ABC pins are 1mm further towards the back face.

Also includes a fix to the Sxxxx variant: the boss was 1mm too short (updated in green)

Then, remove the old PEC12R footprints which has some problems and also didn't specify a particular shaft length.

@aris-kimi Since you reviewed the last one ^_^

I suggest not to squash the commits on this one, as they're each separate things.