[adb client] Fix mdns discovery service registry.

We were getting stale service ip addresses because we weren't
destroying the sdref correctly.

Also, we were leaking the ResolvedServices when removing it from the
ServiceRegistry. Converted them to smart pointers to fix that.

Bug: 153343580

Test: test_adb.py
Change-Id: Ib7c1dbf54937d4ac6d9885cb5f7289bef616d12e