Fix USB device enumeration on Windows 8.1 and Windows 10 (#393)

* Remove USB 2.0 Extension from BOS descriptor.

* Declutter usb.h of unused code.

Now that I'm more confident the USB 2.0 Extensions are only required
for USB 3.0 devices, and there's less mystery around why the change
worked for us, garbage-collect the commented-out descriptor.

board/drivers/usb.h

@@ -281,15 +281,8 @@ uint8_t binary_object_store_desc[] = {
   // BOS header
   BINARY_OBJECT_STORE_DESCRIPTOR_LENGTH, // bLength, this is only the length of the header
   BINARY_OBJECT_STORE_DESCRIPTOR, // bDescriptorType
-  0x40, 0x00, // wTotalLength (LSB, MSB)
-  0x03, // bNumDeviceCaps (USB 2.0 + WebUSB + WinUSB)
-
-  // -------------------------------------------------
-  // USB 2.0 extension descriptor
-  0x07, // bLength, Descriptor size
-  0x10, // bDescriptorType, Device Capability Descriptor Type
-  0x02, // bDevCapabilityType, USB 2.0 extension capability type
-  0x00, 0x00, 0x00, 0x00, // bmAttributes, LIBUSB_BM_LPM_SUPPORT = 2 and its the only option
+  0x39, 0x00, // wTotalLength (LSB, MSB)
+  0x02, // bNumDeviceCaps (WebUSB + WinUSB)
 
   // -------------------------------------------------
   // WebUSB descriptor