ARM: dts: colibri-imx6: remove pinctrl-names orphan

This is not necessary without a pinctrl-0 statement. Remove this
orphan.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>