intel: Drop old romstage main() without asmlinkage

Change-Id: I0d471766fdf46f6e61ac692fc98730a2429f981f
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/15234
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/cpu/intel/romstage.h

@@ -3,9 +3,6 @@
 
 #include <arch/cpu.h>
 
-/* std signature of entry-point to romstage.c */
-void main(unsigned long bist);
-
 void mainboard_romstage_entry(unsigned long bist);
 void * asmlinkage romstage_main(unsigned long bist);