mb/clevo/cml-u: Drop VGA_BIOS_FILE from Kconfig

It doesn't make sense to configure that filename in Kconfig, since the
filename can be changed by the user. So remove it.

Change-Id: I3eed05637da29096bc1d134505d7335db5db1439
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49138
Reviewed-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/mainboard/clevo/cml-u/Kconfig

@@ -66,10 +66,6 @@ config DIMM_SPD_SIZE
 	int
 	default 512
 
-config VGA_BIOS_FILE
-	string
-	default "pci8086,9b41.rom"
-
 config VGA_BIOS_ID
 	string
 	default "8086,9b41"