Fix getComponentName for DomainVerificationProxy

This was preventing the domain verifier from being printed as part of
dumpsys, since PMS checks this to see if the proxy exists.

To avoid future issues, also removs the default interface methods in
favor of just overriding them in the unavailable variant.

Bug: 186665132

Test: manual, dumpsys package dv
Test: atest DomainVerificationProxyTest#nonNullComponentName

Change-Id: Ib8fb5e07b1650a46a9ebb735f9c640877e58cb22