ARM: dts: at91: at91-ariag25: remove leftovers clock definition

The clocks group properties and the clock@0 node have been obsolete for two
years, remove them.

Cc: Sergio Tanzilli <tanzilli@acmesystems.it>
Cc: Douglas Gilbert <dgilbert@interlog.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

arch/arm/boot/dts/at91-ariag25.dts

@@ -34,15 +34,6 @@ memory {
 	};
 
 	clocks {
-		#address-cells = <1>;
-		#size-cells = <1>;
-		ranges;
-
-		main_clock: clock@0 {
-			compatible = "atmel,osc", "fixed-clock";
-			clock-frequency = <12000000>;
-		};
-
 		slow_xtal {
 			clock-frequency = <32768>;
 		};