USB: core: remove polling for /sys/kernel/debug/usb/devices

The latest reference to usbfs_conn_disc_event() removed in
commit fb28d58b

 ("USB: remove CONFIG_USB_DEVICEFS")
in 2012 and now a user poll() waits infinitely for content changes.

Signed-off-by: Sergey Korolev <s.korolev@ndmsystems.com>
Link: https://lore.kernel.org/r/20200809161233.13135-1-s.korolev@ndmsystems.com


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