'clock-output-names' is not used in any of the dts/dtsi files for i.mx.

Remove it from the examples, so that the example and the real usage in the
dtsi files can match.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>