arm64: dts: rockchip: Remove UART2 from RGB30

The Powkiddy RGB30 has no onboard UART header, so remove the reference
to it in the device tree. This was left on by mistake in the initial
commit.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Link: https://lore.kernel.org/r/20231018153357.343142-4-macroalpha82@gmail.com


Signed-off-by: Heiko Stuebner <heiko@sntech.de>