Use TAG_IFD_DEVICE_REMOVED when the reader is removed

When a USB reader is removed then use the new IFD Handler tag
TAG_IFD_DEVICE_REMOVED to signal the fact to the driver.

RFRemoveReader() has a new "flags" parameter.
By default the value REMOVE_READER_NO_FLAG is used.

When the libudev hotplug mechanism detects that a USB device has been
removed then RFRemoveReader() is called with REMOVE_READER_FLAG_REMOVED.
RFRemoveReader() will then use TAG_IFD_DEVICE_REMOVED to tell the
driver that the device has been removed and that no communication with
the device should occur.