Fix syntax error in _HOME_Z and remove xy moves

[MapleLeafMakers]

• Fixes a typo that causes a parse error in the new _HOME_Z macro
• Removes code to center the toolhead before homing Z

Rationale:

• There's no reason to move X or Y during a Z home, since the toolhead is not required (or in the way) during homing Z.
• Because there is no reason for it, to do it would be "unexpected behaviour"
• it risks dragging the nozzle across the bed, potentially doing damage.