BUG-1742: do not use RemovalListener

RemovalListener with softvalues does not give us the value which expired
(rightly so), so we need to use a phantom reference to remove the
registration.

Change-Id: Ia693bd3b738528446d497fca54d2ff6e52e8d7f2
Signed-off-by: Robert Varga <rovarga@cisco.com>