usb: remove commented out dma wrappers

These wrappers have never seen use and have been commented out
for a long time.  Remove them for good.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20190903084615.19161-6-hch@lst.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>