Remove urb request size maximum.

The 16kB maximum for transfers was removed from
the kernel in 3.3. Devio has since supported
arbitrary transfer sizes through scatter gather.

See the following kernel patches for context:
"USB: change the memory limits in usbfs URB submission"
"usbdevfs: Use scatter-gather lists for large bulk transfers"

Bug: 67683483
Test: Run usb_async_test app with USB3 : 38MB/s -> 300MB/s
Change-Id: Ia52440cb725561b0f1db1a75aa1b8ab952585826