simplify Clear() in Window and its derivatives

it removes argument responsible for immediate refreshing.
since after all calls that were refreshing screen there was
call to Refresh() anyway, this switch doesn't make much sense.

src/visualizer.cpp

@@ -120,7 +120,7 @@ void Visualizer::Update()
 	if (data < 0) // no data available in fifo
 		return;
 	
-	w->Clear(0);
+	w->Clear();
 #	ifdef HAVE_FFTW3_H
 	Config.visualizer_use_wave ? DrawSoundWave(buf, data) : DrawFrequencySpectrum(buf, data);
 #	else