Qt::Appearance: don't assign values to enumerators

The compiler does that for us. This makes the enum look like an enum
again. A non-flags enum shouldn't have intializers of the form 0xNNNN,
as that makes it looks like flags.

Found in API review.

Pick-to: 6.5
Change-Id: If49e94cdad719b7dc9e8a7b17f6883dc789e62d6
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>

src/corelib/global/qnamespace.h

@@ -47,9 +47,9 @@ namespace Qt {
     };
 
     enum class Appearance {
-        Unknown = 0x0000,
-        Light   = 0x0001,
-        Dark    = 0x0002
+        Unknown,
+        Light,
+        Dark,
     };
 
     enum MouseButton {