Deprecate org.opendaylight.controller.sal.common.util.Futures

We use guava throughout -- and those are better.

Change-Id: I0013f8fc0c10742791159abdf151662eaae5629f
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "Deprecate org.opendaylight.controller.sal.common.util.Futures"