Some private classes had a q_ptr pointer shadowing
the QObjectPrivate::q_ptr pointer. Q_Q casts the QObjectPrivate::q_ptr
pointer to match the public class so there is no need to store a
different pointer.

Change-Id: I8f5c4323b1dcf45a9796c0dd9f522bdbc63add18
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>