include/console/system76_ec.h: Remove unused <stddef.h>

Change-Id: I3ac96786b4bbf7c8b3a8b57f58df396b1b754bd3
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/83953
Reviewed-by: Martin L Roth <gaumless@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/console/system76_ec.h

@@ -3,7 +3,6 @@
 #ifndef CONSOLE_SYSTEM76_EC_H
 #define CONSOLE_SYSTEM76_EC_H 1
 
-#include <stddef.h>
 #include <stdint.h>
 
 void system76_ec_init(void);