arm: dts: k3-am654: remove duplicate mcu_uart0 node

With the Linux and U-Boot board dtb files unified we now have a
duplicate mcu_uart0 node. Remove it

Tested-by: Tom Rini <trini@konsulko.com>
Signed-off-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Nishanth Menon <nm@ti.com>