When disconnect()ing through a QMetaObject::Connection, if the
QObjectPrivate::Connection contains a slot object, deref it, so
that it will be destroyed before the next run of cleanConnectionList.
Previously, a copy of the functor passed to connect() was kept until
QObjectPrivate::cleanConnectionLists was called (by adding a new signal,
or the sender was destroyed), even after a successful call to
disconnect(). That is, we were keeping that copy allocated without
any good reason.
Change-Id: Ie6074ea797df1611cb995dec07c5b5a742360833
Reviewed-by: Olivier Goffart <ogoffart@woboq.com>