usb: gadget: f_accessory: remove unused acc_bind_config function

The Android Accessory function driver has a function without any callers,
resulting in a harmless build warning:

drivers/usb/gadget/function/f_accessory.c:1182:12: warning: 'acc_bind_config' defined but not used [-Wunused-function]

Removing the function and associated code gets rid of the warning
and has no other effect.

Fixes: d588b95d ("usb: gadget: accessory: Add Android Accessory function")
Cc: Anson Jacob <ansonjacob.aj@gmail.com>
Cc: Badhri Jagan Sridharan <Badhri@google.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>