arm64: dts: ti: k3-am625-sk: Remove M4 mailbox node redefinition

This node is already defined in the included k3-am62x-sk-common.dtsi.
Remove this redefinition.

Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20241203164031.20211-1-afd@ti.com


Signed-off-by: Nishanth Menon <nm@ti.com>