ARM: dts: ti: keystone: k2g: Remove ti,system-reboot-controller property

The property ti,system-reboot-controller is no longer needed as the reboot
handler is now always registered. Remove this property.

While here remove the comment about delete-property, all K2G platforms use
PMMC, and it wasn't good advice anyway.
Signed-off-by: Andrew Davis <afd@ti.com>
Link: https://lore.kernel.org/r/20240326223730.54639-4-afd@ti.comSigned-off-by: Nishanth Menon <nm@ti.com>

arch/arm/boot/dts/ti/keystone/keystone-k2g.dtsi

@@ -256,11 +256,6 @@ msgmgr: mailbox@2a00000 {
 
 		pmmc: system-controller@2921c00 {
 			compatible = "ti,k2g-sci";
-			/*
-			 * In case of rare platforms that does not use k2g as
-			 * system master, use /delete-property/
-			 */
-			ti,system-reboot-controller;
 			mbox-names = "rx", "tx";
 			mboxes = <&msgmgr 5 2>,
 				<&msgmgr 0 0>;