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/mt7621_totolink_a7000r.dts

@@ -17,11 +17,6 @@
 		led-upgrade = &led_sys;
 	};
 
-	memory@0 {
-		device_type = "memory";
-		reg = <0x0 0x8000000>;
-	};
-
 	chosen {
 		bootargs = "console=ttyS0,57600";
 	};