UWP: Remove external camera check on rotate

This as noted by other issues prevents the videoFrame from being set if there's an external camera, causing exceptions.

This closes #396 and part of #389

Source/ZXing.Net.Mobile.WindowsUniversal/ZXingScannerControl.xaml.cs

@@ -560,7 +560,7 @@ private void buttonToggleFlash_Click(object sender, RoutedEventArgs e)
         private async Task SetPreviewRotationAsync(IMediaEncodingProperties props)
         {
             // Only need to update the orientation if the camera is mounted on the device.
-            if (mediaCapture == null || externalCamera)
+            if (mediaCapture == null)
                 return;
 
             // Calculate which way and how far to rotate the preview.