boards: nordic: Do not enable hw-flow-control on console

Like in all other legacy boards, hw-flow-control should not be
enabled for console UART. With hw-flow-control sample stuck
during printing some initial information and sample appears to
be not working correctly unless com port is opened.

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>