BCM27XX_DT: Delete 'stdout-path' property

The 'stdout-path' property introduced upstream changes the behaviour
on a non-Bluetooth Pi by enabling a console on UART0 when the user
may not want one. The boot order is such that /dev/console ends up
on the serial port instead of tty0.

Delete the property in downstream DTBs to retrurn to the previous
behaviour of only enabling consoles selected in cmdline.txt.

See: https://github.com/raspberrypi/linux/issues/2436



Signed-off-by: Phil Elwell <phil@raspberrypi.org>