mindpx-v2 Remove GPIO_RC_OUT and vetted RC_IN wiring

   Removed the legacy FMUv4 define that was activating a nonexistent
   pull up and on some HW driving the PPM_IN aka RC_IN aka SPEKTRUM_RX
   to VDD.

   Also detailed the connections of this pins for the board.

   The simplest connection is RC_IN to a timer capture pin
   and a UART.
   In this case the UART_RX pin and just be left as is.
   While the pin can be configured as the PPM_IN (Timer capture)
   or as SPEKTRUM_RX_AS_GPIO_OUTPUT to use it as and GPIO to
   facilitate binding.

  Renamed the macros and defines to be more explicit as to what
  Is being done and the sense of the parameters