tree: Remove unused <string.h>

Change-Id: I9ed1a82fcd3fc29124ddc406592bd45dc84d4628
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82666
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Yidi Lin <yidilin@google.com>

src/ec/google/chromeec/i2c_tunnel/i2c_tunnel.c

@@ -6,7 +6,7 @@
 #include <device/device.h>
 #include <device/path.h>
 #include <stdio.h>
-#include <string.h>
+
 #include "chip.h"
 
 #define CROS_EC_I2C_TUNNEL_HID		"GOOG0012"