ARM: at91/dt: remove leftovers clock definition

The clocks group properties and the clock@0 node are useless, remove them
to avoid copy pasting in future device trees.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>

arch/arm/boot/dts/at91rm9200ek.dts

@@ -21,15 +21,6 @@
 	};
 
 	clocks {
-		#address-cells = <1>;
-		#size-cells = <1>;
-		ranges;
-
-		main_clock: clock@0 {
-			compatible = "atmel,osc", "fixed-clock";
-			clock-frequency = <18432000>;
-		};
-
 		slow_xtal {
 			clock-frequency = <32768>;
 		};