Include all the necessary pieces to get the final Z position after
probing the bed, and add commentary about other possible changes.

Just set up the pin. Don't move to a random position.

Simplify servo::move()
* servo::move() does not need the pin parameter - The pin is set during servo_init() with attach().
* servo::move() does not need a return value.

SERVO_LEVELING is the wrong condition to deactivate the servos.

Remove some temporary (Servo *) variables.
SanityCheck for the servo indexes.

Updates to `set_homing_bump_feedrate`:
- Move the string into Program Memory, reduce length by 31 bytes
- Use an auto to get the divisor, adjust it on error
- Set feedrate once, at the end

- Change suggested at
https://github.com/MarlinFirmware/Marlin/issues/2482#issuecomment-123553
266

The compiler may be able to optimize if it knows an array won’t be
changing.

`gcode_M84` only needs to call `finishAndDisableSteppers`, which calls
all the other functions.

- Documentation solution for #2476

Assuming #2470 fixed up the main issue.

- Update prepare_move_delta to take a target argument
- Add Delta support to plan_arc

Patch servos code for move

- Have `Servo::attach` explicitly return -1 if it fails
- Check for -1 in `Servo::move` because `servoIndex` might be 0
- Make `attach` / `detach` calls conditional on `SERVO_LEVELING`
- Move `SERVO_LEVELING` define to `Conditionals.h`

Elsewhere DRYRUN turns off the heating elements
and ignores constraints on them.

Here, whenever motion is entered into the planner,
if DRY RUN is set, we instantly act as if the E_AXIS
is in the desired final position.

to make clear - it's not a question but an order.