macos: force pixel format without depth/stencil

We don't need either depth or stencil buffers, so we want a pixel format
without them so that things like glClear() can do less work.

gdk/macos/gdkmacosglcontext.c

@@ -330,6 +330,8 @@ create_pixel_format (int      major,
   CGLPixelFormatAttribute attrs[] = {
     kCGLPFAOpenGLProfile, (CGLPixelFormatAttribute)kCGLOGLPVersion_Legacy,
     kCGLPFAAllowOfflineRenderers, /* allow sharing across GPUs */
+    kCGLPFADepthSize, 0,
+    kCGLPFAStencilSize, 0,
     kCGLPFAColorSize, 24,
     kCGLPFAAlphaSize, 8,
     0