Drop ROMCC code and header guards

Change-Id: I730f80afd8aad250f26534435aec24bea75a849c
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37334
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: HAOUAS Elyes <ehaouas@noos.fr>

src/cpu/x86/16bit/entry16.inc

@@ -29,13 +29,10 @@
 
 #include <arch/rom_segs.h>
 
-#if !CONFIG(ROMCC_BOOTBLOCK) || \
-    CONFIG(SIPI_VECTOR_IN_ROM)
 /* Symbol _start16bit must be aligned to 4kB to start AP CPUs with
  * Startup IPI message without RAM.
  */
 .align 4096
-#endif
 .code16
 .globl _start16bit
 .type _start16bit, @function