usb: gadget: uac2: Drop unused device qualifier descriptor

This descriptor is never used. Currently device qualifier
descriptor is generated by compossite code so no need to
keep it in function file.

Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Krzysztof Opasiak <kopasiak90@gmail.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>