Mark the QDesktopServices::StorageLocation enum as obsolete in the docs

The enum was already deprecated but the documentation still listed it
so now it is correctly obsoleted.

Change-Id: I9d64fe58a5e70de7161928da2d09b4532d450274
Reviewed-by: Liang Qi <liang.qi@digia.com>

src/gui/util/qdesktopservices.cpp

@@ -250,6 +250,8 @@ void QDesktopServices::unsetUrlHandler(const QString &scheme)
 /*!
     \enum QDesktopServices::StandardLocation
     \since 4.4
+    \obsolete
+    Use QStandardPaths::StandardLocation
 
     This enum describes the different locations that can be queried by
     QDesktopServices::storageLocation and QDesktopServices::displayName.