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/drivers/intel/gma/acpi.c

@@ -2,7 +2,7 @@
 
 #include <acpi/acpigen.h>
 #include <stdio.h>
-#include <string.h>
+
 #include "i915.h"
 
 void

src/drivers/intel/usb4/retimer/retimer.c

@@ -8,7 +8,7 @@
 #include <drivers/usb/acpi/chip.h>
 #include <gpio.h>
 #include <stdio.h>
-#include <string.h>
+
 #include "chip.h"
 #include "retimer.h"