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>