board: phytec: imx8mm-phycore: Remove duplicate binman node

The binman node is part of the imx8mm-u-boot.dtsi file which
is duplicated in phycore-imx8mm-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>