src: Remove unused include <string.h>

Change-Id: Ic6b66dd8fa387e67bb0ce609fb7e2553eeb66b3c
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37888
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/lib/hexstrtobin.c

@@ -13,7 +13,6 @@
 
 #include <ctype.h>
 #include <lib.h>
-#include <string.h>
 
 size_t hexstrtobin(const char *str, uint8_t *buf, size_t len)
 {