QSharedPointer: Remove support code for tracking weak-pointer

In Qt 6, it is no longer possible to create a weak pointer from a plain
QObject pointer.
Consequently, we don't need the work-aronuds introduced for QTBUG-22622.
Except that we still need to keep the functions as they are exported.
Mark them as QT6_ONLY, so that they'll be gone automatically come Qt 6.

Amends e40320c552.

Change-Id: I568da04008374c891a111eee49f6679dabdfdee4
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

src/corelib/tools/qsharedpointer.cpp

@@ -1422,6 +1422,7 @@
 
 QT_BEGIN_NAMESPACE
 
+QT6_ONLY(
 /*!
     \internal
     This function is called for a just-created QObject \a obj, to enable
@@ -1429,7 +1430,9 @@ QT_BEGIN_NAMESPACE
  */
 void QtSharedPointer::ExternalRefCountData::setQObjectShared(const QObject *, bool)
 {}
+)
 
+QT6_ONLY(
 /*!
     \internal
     This function is called when a QSharedPointer is created from a QWeakPointer
@@ -1442,6 +1445,7 @@ void QtSharedPointer::ExternalRefCountData::checkQObjectShared(const QObject *)
     if (strongref.loadRelaxed() < 0)
         qWarning("QSharedPointer: cannot create a QSharedPointer from a QObject-tracking QWeakPointer");
 }
+)
 
 QtSharedPointer::ExternalRefCountData *QtSharedPointer::ExternalRefCountData::getAndRef(const QObject *obj)
 {

src/corelib/tools/qsharedpointer_impl.h

@@ -116,8 +116,10 @@ namespace QtSharedPointer {
 
 #ifndef QT_NO_QOBJECT
         Q_CORE_EXPORT static ExternalRefCountData *getAndRef(const QObject *);
+        QT6_ONLY(
         Q_CORE_EXPORT void setQObjectShared(const QObject *, bool enable);
-        Q_CORE_EXPORT void checkQObjectShared(const QObject *);
+        )
+        QT6_ONLY(Q_CORE_EXPORT void checkQObjectShared(const QObject *);)
 #endif
         inline void checkQObjectShared(...) { }
         inline void setQObjectShared(...) { }
@@ -499,7 +501,6 @@ private:
 #ifdef QT_SHAREDPOINTER_TRACK_POINTERS
         internalSafetyCheckAdd(d, ptr);
 #endif
-        d->setQObjectShared(ptr, true);
         enableSharedFromThis(ptr);
     }
 
@@ -527,12 +528,10 @@ private:
                 tmp = o->strongref.loadRelaxed();  // failed, try again
             }
 
-            if (tmp > 0) {
+            if (tmp > 0)
                 o->weakref.ref();
-            } else {
-                o->checkQObjectShared(actual);
+            else
                 o = nullptr;
-            }
         }
 
         qt_ptr_swap(d, o);