Enable volume UI for TVs using Absolute Volume Control.

HdmiControlService now sets FLAG_SHOW_UI when calling AudioService APIs
on a TV using Absolute Volume Control.

With UI being shown when using Absolute Volume Control, hiding volume UI
is only necessary when system audio mode is enabled, but Absolute Volume
Control is not. This is covered by the check for full volume behavior in
AudioService#sendVolumeUpdate, so the other TV-specific checks can be
removed.

Bug: 231430528
Test: manual
Change-Id: I0579b3af77abe2559b64574e162021320cfb9100