Doc: Don't show a description for omitted SH_ComboBox_UseNativePopup enum item

\omitvalue does not allow a description of an enum item, so move
the description as a comment to the enum declaration.

Change-Id: I4192b16e41b704cbad66c0eeafcb141087d2ba65
Reviewed-by: Martin Smith <martin.smith@digia.com>

src/widgets/styles/qstyle.cpp

@@ -1750,8 +1750,7 @@ void QStyle::drawItemPixmap(QPainter *painter, const QRect &rect, int alignment,
     \value SH_ComboBox_Popup  Allows popups as a combobox drop-down
         menu.
 
-    \omitvalue SH_ComboBox_UseNativePopup  Whether we should use a native popup.
-        Only supported for non-editable combo boxes on Mac OS X so far.
+    \omitvalue SH_ComboBox_UseNativePopup
 
     \value SH_Workspace_FillSpaceOnMaximize  The workspace should
         maximize the client area.

src/widgets/styles/qstyle.h

@@ -702,6 +702,8 @@ public:
         SH_ToolTip_FallAsleepDelay,
         SH_Widget_Animate,
         SH_Splitter_OpaqueResize,
+        // Whether we should use a native popup.
+        // Only supported for non-editable combo boxes on Mac OS X so far.
         SH_ComboBox_UseNativePopup,
         // Add new style hint values here