UI: Compact ClearVolumeControls()

Closes obsproject/obs-studio#1296

UI/window-basic-main.cpp

@@ -409,12 +409,8 @@ void OBSBasic::UpdateVolumeControlsPeakMeterType()
 
 void OBSBasic::ClearVolumeControls()
 {
-	VolControl *control;
-
-	for (size_t i = 0; i < volumes.size(); i++) {
-		control = volumes[i];
-		delete control;
-	}
+	for (VolControl *vol : volumes)
+		delete vol;
 
 	volumes.clear();
 }