usb: gadget: Remove final remnants of CONFIG_USB_DEVICE

The lone user of the legacy USB device framework have been removed for
some time. Remove the final parts of the code that were missed.

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Link: https://lore.kernel.org/r/20250227205101.4127604-1-trini@konsulko.com
Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
7 files changed