idex_mode would swap the X and dual-carriage rail in some cases
(homing), but not in others. As such, the position calculation was
correct while homing, but incorrect for the second carriage during
normal moves. This commit fixes homing to work without swapped rails,
removes the swapping of rails while homing, and removes the ability to
swap rails (as it is now no longer used). Fix has been tested in a
Hybrid_CoreXY IDEX printer (Voron Double Dragon). Hybrid_CoreXZ has
identical changes and is similar enough that I am confident it will work
as intended. Changes to cartesion seem simple enough, but would benefit
from someone running a couple of tests.
Signed-off-by: Frans-Willem Hardijzer <fw@hardijzer.nl>