USB: dma: remove unused function prototype

usb_buffer_map_sg() and usb_buffer_unmap_sg() have no definition
since the beginning of v5.4. The rest are gone from 2.6.12.

Signed-off-by: Randy Li <ayaka@soulik.info>
Link: https://lore.kernel.org/r/20230914172336.18761-2-ayaka@soulik.info
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/usb.h

@@ -1823,22 +1823,6 @@ void *usb_alloc_coherent(struct usb_device *dev, size_t size,
 void usb_free_coherent(struct usb_device *dev, size_t size,
 	void *addr, dma_addr_t dma);
 
-#if 0
-struct urb *usb_buffer_map(struct urb *urb);
-void usb_buffer_dmasync(struct urb *urb);
-void usb_buffer_unmap(struct urb *urb);
-#endif
-
-struct scatterlist;
-int usb_buffer_map_sg(const struct usb_device *dev, int is_in,
-		      struct scatterlist *sg, int nents);
-#if 0
-void usb_buffer_dmasync_sg(const struct usb_device *dev, int is_in,
-			   struct scatterlist *sg, int n_hw_ents);
-#endif
-void usb_buffer_unmap_sg(const struct usb_device *dev, int is_in,
-			 struct scatterlist *sg, int n_hw_ents);
-
 /*-------------------------------------------------------------------*
  *                         SYNCHRONOUS CALL SUPPORT                  *
  *-------------------------------------------------------------------*/