boards: decawave_dwm3001cdk: remove CDC ACM configuration

This board has a built-in debug adapter that provides a serial
connection to the host. This is mentioned in the board documentation.
The SoC pins P0.15 (RX) and P0.19 (TX) are connected to the debug
adapter pins TXD and RXD, respectively. This board should not configure
any other serial connection by default.

Update the board documentation accordingly.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>