USBPhyHw: remove mbed.h inclusion

Remove user facing header file, it should not be included within a library. The header itself does not need anything from Mbed.

It could possibly fail if targets which implement usb are not including what is required for their implementation.

Author: 0xc0170

targets/TARGET_Freescale/USBPhyHw.h

@@ -17,7 +17,6 @@
 #ifndef USBPHYHW_H
 #define USBPHYHW_H
 
-#include "mbed.h"
 #include "USBPhy.h"