Revert "windows opengl: Set PFD_DOUBLEBUFFER even for single buffer rendering"

This reverts commit 6fd71992. Kendy says the
original problem can't be reproduced anymore, and most unexpected flickering
goes away with this for my nvidia card.

Also, it's a good idea in general to keep PFD_DOUBLEBUFFER and
WGL_DOUBLE_BUFFER_ARB in sync, which is now the case.

Change-Id: I7a809d1c85be4206c01720d5de9b0a5617a59c87

vcl/source/opengl/OpenGLContext.cxx

@@ -837,9 +837,8 @@ bool OpenGLContext::ImplInit()
         0, 0, 0                         // Layer Masks Ignored
     };
 
-    // interestingly we need this flag being set even if we use single buffer
-    // rendering - otherwise we get errors with virtual devices
-    PixelFormatFront.dwFlags |= PFD_DOUBLEBUFFER;
+    if (mbUseDoubleBufferedRendering)
+        PixelFormatFront.dwFlags |= PFD_DOUBLEBUFFER;
 
     PixelFormatFront.dwFlags |= PFD_DRAW_TO_WINDOW;