clean up

- remove TUD_WEBUSB_URL_DESCRIPTOR to avoid flexible array member (C++
forbid in strict mode)
- remove unused TUD_DESC_STRLEN/TUD_DESC_STR_HEADER/TUD_DESC_STR_HEADER

examples/device/msc_dual_lun/src/usb_descriptors.c

@@ -147,8 +147,8 @@ uint16_t const* tud_descriptor_string_cb(uint8_t index)
     }
   }
 
-  // first byte is len, second byte is string type
-  _desc_str[0] = TUD_DESC_STR_HEADER(chr_count);
+  // first byte is length (including header), second byte is string type
+  _desc_str[0] = (TUSB_DESC_STRING << 8 ) | (2*chr_count + 2);
 
   return _desc_str;
 }