libusb: Fix usb_devs_lock mutex use after free in libusb_init error path

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
hotplug: Remove device from usb_devs before signalling its removal

If we write the remove event to the pipe before doing the list_del,
in theory another thread can process the event and unref the device before
it has been removed from usb_devs.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>