ARM: dts: omap: Drop references to opp.txt

opp.txt is getting removed with the OPP binding converted to DT schema.
As it is unusual to reference a binding doc from a dts file, let's just
remove the reference.

Cc: "Benoît Cousson" <bcousson@baylibre.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>

arch/arm/boot/dts/omap34xx.dtsi

@@ -24,7 +24,6 @@ cpu: cpu@0 {
 		};
 	};
 
-	/* see Documentation/devicetree/bindings/opp/opp.txt */
 	cpu0_opp_table: opp-table {
 		compatible = "operating-points-v2-ti-cpu";
 		syscon = <&scm_conf>;

arch/arm/boot/dts/omap36xx.dtsi

@@ -29,7 +29,6 @@ cpu: cpu@0 {
 		};
 	};
 
-	/* see Documentation/devicetree/bindings/opp/opp.txt */
 	cpu0_opp_table: opp-table {
 		compatible = "operating-points-v2-ti-cpu";
 		syscon = <&scm_conf>;