imx: imx8mm: imx8mm-kontron-n801x-s: Fix binman error

The binman node is part of the imx8mm-u-boot.dtsi file which
is duplicated in imx8mm-kontron-n801x-s-u-boot.dtsi and causes
a build error.  Remove the duplicate.

Fixes: 3cbb31f0e848 ("arm64: dts: imx8mm: use common binman configuration")
Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>