riscv: dts: binman.dtsi: Drop filename property for proper U-Boot

Drop filename property for proper U-Boot entry since binman takes
"u-boot-nodtb.bin" as the default filename for u-boot-nodtb entries.

This follows efe9c12322 ("riscv: dts: binman.dtsi: Switch to
u-boot-nodtb entry for proper U-Boot") to clean binman.dtsi up.

Signed-off-by: Yao Zi <ziyao@disroot.org>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>

arch/riscv/dts/binman.dtsi

@@ -42,7 +42,6 @@
 					load = /bits/ 64 <CONFIG_TEXT_BASE>;
 
 					uboot_blob: u-boot-nodtb {
-						filename = "u-boot-nodtb.bin";
 					};
 				};
 #else