usb: bootm: Drop old USB-device-removal code

USB is stopped using driver model now, in dm_remove_devices_flags() in
announce_and_cleanup() at the top of this file.

The usb_stop() call actually unbinds devices.

When a USB device is unbound, it causes any bootflows attached to it to
be removed, via a call to bootdev_clear_bootflows() from
bootdev_pre_unbind(). This obviously makes it impossible to boot the
bootflow.

However, when booting a bootflow that relies on USB, usb_stop() is
called, which unbinds the device. At that point any information
attached to the bootflow is dropped.

This is quite risky since the contents of freed memory are not
guaranteed to remain unchanged. Depending on what other options are
done before boot, a hard-to-find bug may crop up.

Drop the call to this old function.

Leave the netconsole call there, since this needs conversion to
driver model.

Signed-off-by: Simon Glass <sjg@chromium.org>
Suggested-by: Shantur Rathore <i@shantur.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>