Unify IOS/OS X code in OutputDevice::DrawTransformedBitmapEx()

The way that we apply the alpha mask in DrawTransformedBitmapEx should
be handled in the same way, regardless of the platform. As it turns out,
the OS X/iOS way is quite correct and, as a bonus, the code is far more
clear. There is no need to do things differently, so let's use the OS X
approach.

Change-Id: Ib0ac72ddc549367462e84639b74e4bb148128cd5

vcl/source/outdev/bitmap.cxx

@@ -519,13 +519,10 @@ void OutputDevice::DrawTransformedBitmapEx(
             {
                 // parts will be uncovered, extend aTransformed with a mask bitmap
                 const Bitmap aContent(aTransformed.GetBitmap());
-#if defined(MACOSX) || defined(IOS)
+
                 AlphaMask aMaskBmp(aContent.GetSizePixel());
                 aMaskBmp.Erase(0);
-#else
-                Bitmap aMaskBmp(aContent.GetSizePixel(), 1);
-                aMaskBmp.Erase(Color(COL_BLACK)); // #122758# Initialize to non-transparent
-#endif
+
                 aTransformed = BitmapEx(aContent, aMaskBmp);
             }