Remove Plan's WP Radius field for Copter and Rover

[rmackay9]

Most Copter and Rover users really don't need to update the WP Radius value but because it is displayed on the PLAN screen they tend to and it can lead to the vehicle getting stuck if set too low. An example of such a support issue can be found here.

Copter's extended tuning screen and Rover's Basic tuning screen have fields that allow users to change this on the fly.

By the way, adding to the confusion is that the Plan's screen's WP Radius does not match the Copter or Rover's WP Radius value shown on the extended or basic tuning screens.

Let's remove the Loiter Radius field too because it's non-functional for Copter and Rover.