iOS: Don't set background color when debugging window management

It will fill the view in some cases, obscuring what Qt draws.

Change-Id: I9ca00dddd829a28fb2cb3b009bfd3223f85ef7cb
Reviewed-by: Jake Petroules <jake.petroules@qt.io>

src/plugins/platforms/ios/quiview.mm

@@ -95,7 +95,6 @@
             #define colorWithBrightness(br) \
                 [UIColor colorWithHue:hue saturation:0.5 brightness:br alpha:1.0].CGColor
 
-            self.layer.backgroundColor = colorWithBrightness(0.5);
             self.layer.borderColor = colorWithBrightness(1.0);
             self.layer.borderWidth = 1.0;
         }