src: Remove redundant <rules.h> and <commonlib/bsd/compiler.h>

<rules.h> and <commonlib/bsd/compiler.h> are always automatically
included in all compilation units by the build system

Change-Id: I9528c47f4b7cd22c5a56d6a59b3bfe53197cc4d8
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/60932
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Felix Held <felix-coreboot@felixheld.de>

src/lib/string.c

@@ -1,6 +1,5 @@
 #include <assert.h>
 #include <ctype.h>
-#include <rules.h>
 #include <string.h>
 #include <stddef.h>
 #include <stdlib.h>