js: Remove adjusting with performance.now
js: Remove adjusting with performance.now

Adjusting timing with performance.now was introduced at
39cc94a3dd00dbf39fd901462aced964fa3649d6, but noise was not
reduced as expected. To make matters worse, this was the cause
of the audio delay.

Fixes hajimehoshi/ebiten#959.

hajimehoshi/oto,hajimehoshi/oto