ramips: dts: drop memory nodes

mt7621 and mt7628 now have the ability to detect memory size
automatically.
Drop memory nodes and let kernel determine memory size.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>

target/linux/ramips/dts/mt7628an_wiznet_wizfi630s.dts

@@ -14,11 +14,6 @@
 		bootargs = "console=ttyS1,115200";
 	};
 
-	memory@0 {
-		device_type = "memory";
-		reg = <0x0 0x8000000>;
-	};
-
 	aliases {
 		led-boot = &led_run;
 		led-failsafe = &led_run;