brcm63xx: drop linux,part-probe usage where possible

It was present as 4.4 compatibility, but since we now use 4.9 or later
with the new upstream solution, we don't need it anymore.

Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>

target/linux/brcm63xx/dts/usr9108.dts

@@ -30,8 +30,6 @@
 &pflash {
 	status = "ok";
 
-	linux,part-probe = "bcm63xxpart";
-
 	partitions {
 		compatible = "fixed-partitions";
 		#address-cells = <1>;