ARM: dts: imx6dl-plym2m: remove touchscreen-size-* properties

Remove touchscreen-size-* properties.  This values are not correct, event if it
works with ts_test tool, it fails to work properly with weston.

Signed-off-by: Oleksij Rempel <o.rempel@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>