usb: musc: Remove unused list 'buffers'

Remove the unused list head 'buffers' and the
'struct free_record' which is also unused below it.

To me it looks like this has always been unused, but I've
not dug into why.

Build test only.

Signed-off-by: "Dr. David Alan Gilbert" <linux@treblig.org>
Link: https://lore.kernel.org/r/20240504150315.77598-1-linux@treblig.org


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