Override has_pilot_input_for_override_clear() to use Sub's joystick
axes (forward, lateral, yaw, plus throttle mapped to vertical thrust)
instead of the Copter-style roll/pitch/yaw/throttle set.
This removes the need for the pointer to the first flight mode, and
removes the undefined behavior resulting from indexing past that first
flight mode and hoping the others follow (though this is unlikely to
pose a problem in practice).
Saves a few bytes of RAM and flash as the pointer is no longer needed
and code is no longer necessary to set it up.
Also fixes the bounds check condition of that array to match its size so
there is no longer the possibility of indexing one past it.
Tatsuya Yamaguchi
Thomas Watson
Peter Barker
Henry Wurzburg