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/include/stdbool.h

@@ -5,11 +5,8 @@
 
 #include <stdint.h>
 
-#ifdef __ROMCC__
-typedef uint8_t bool;
-#else
+
 typedef _Bool   bool;
-#endif
 #define true    1
 #define false   0