[pm/metrics] do not log package name for adb installations

Per privacy requirements, we will not log package name if the
installation is initiated from adb.

Test: manual with adb install
Test: $ ./out/host/linux-x86/bin/statsd_testdrive 263
event_metrics {
  data {
    elapsed_timestamp_nanos: 630320497997
    atom {
      package_installer_v2_reported {
        is_incremental: true
        package_name: ""
        duration_millis: 567
        return_code: 1
      }
    }
  }
}

BUG: 152913040
Change-Id: I147358e59bf6a43fc76b6721ec1a415167b305d7