usb: gadget: storage: Remove unused function pointer typedef fsg_routine_t

Remove the 'fsg_routine_t' typedef as it is not used.

Signed-off-by: Chen Lin <chen.lin5@zte.com.cn>
Link: https://lore.kernel.org/r/1613384130-3028-1-git-send-email-chen45464546@163.com


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