Get rid of the getter for QObjectPrivate::threadData

The dependent changes have now landed.

Change-Id: I502377ab5603d67ada9e5577de1abfccdfa0fa09
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/kernel/qobject_p.h

@@ -374,7 +374,6 @@ public:
     }
 public:
     ExtraData *extraData;    // extra data set by the user
-    QThreadData *getThreadData() const { return threadData.loadAcquire(); }
     // This atomic requires acquire/release semantics in a few places,
     // e.g. QObject::moveToThread must synchronize with QCoreApplication::postEvent,
     // because postEvent is thread-safe.