ARIA2 Remove "when there is a visual cue to this effect." from objective.

The application of ARIA2 should not be limited whether "there is a visual cue to this effect." Because there could be audio or other sensory cues if authors use CSS or JavaScript. Also, the "Tests" procedures don't check whether "there is a visual cue to this effect."

We should remove "there is a visual cue to this effect." from the objective.