soc/intel/broadwell/romstage: Clean up unused bist variable

Checking BIST is done in the bootblock.

Change-Id: I3ea2eb6a37c038f7348f0abd2056eee5c07bdb9d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/32757
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/soc/intel/broadwell/include/soc/romstage.h

@@ -22,7 +22,6 @@
 
 struct chipset_power_state;
 struct romstage_params {
-	unsigned long bist;
 	struct chipset_power_state *power_state;
 	struct pei_data pei_data;
 };