mx6qsabreauto: Remove imx6q-sabreauto.dts

mx6qsabreauto: Remove imx6q-sabreauto.dts

Commit fa9c021632473 ("mx6: add example DTB for mx6qsabreauto") introduced
'imx6q-sabreauto.dts' but it adds no real value as the dts file only contains
the 'model' and 'compatible' strings.

After this commit the final binary is also changed from 'u-boot.imx' to
'u-boot-dtb.imx', which may confuse users.

So revert it until a more complete and useful device tree could be provided.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>