home.c: don't move to zero after homing to max endstop.

This can be counterproductive if the actual zero point is
outside the available build room. For example, if an additional
bed probing is going to happen. It also costs quite some
time on the Z axis. If you actually  want this behaviour,
send a simple G0 XYZ after homing.
home.c: no need to turn off Z axis here.

This is done in dda.c already, see dda.c, line 678.