bluetooth: remove Kconfig options CONFIG_BT_*_ON_DEV_NAME

Follow up on commit bfd45e5b
("drivers: remove Kconfig option CONFIG_UART_CONSOLE_ON_DEV_NAME")
Remove Kconfig options
CONFIG_BT_UART_ON_DEV_NAME and CONFIG_BT_MONITOR_ON_DEV_NAME
since all UART drivers are converted to devicetree and we can just use
DEVICE_DT_GET(DT_CHOSEN(zephyr_bt_uart)) and
DEVICE_DT_GET(DT_CHOSEN(zephyr_bt_mon_uart)).

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