Hide connected ethernet row when ethernet settings flag is enabled

The connected ethernet row is the legacy UI item that is shown when an
ethernet connection is available.

When the new ethernet settings are available, this row should be hidden.

Flag: com.android.settings.connectivity.ethernet_settings

Bug: b/408439324

Test: Manual check on a Pixel tablet
Change-Id: Idefca0c839a736d3c927018bb68f03afbc57ac09