Remove TODO to allow compilation checker script to run for Cpp snippet

Author: hugueskamba

docs/api/usb/USBHID.md

@@ -12,7 +12,7 @@ You can use the USBHID class to turn an Mbed board into an HID (Human Interface
 
 ### main.cpp   
 
-```C++ TODO
+```C++
 #include <stdio.h>
 
 #include "mbed.h"