signal: Removes assertion in destructor
signal: Removes assertion in destructor

The assertion that checked that the SignalBasePrivate member
was a unique shared_ptr sometimes failed in tests. This is due
to the fact that SignalSubscribers keep a weak_ptr to that
object and might have it locked at the same time of the
destructor call.

Change-Id: Ia7bd4b6f249a4526f379d152fc8c49cfd719c09f
Reviewed-on: http://gerrit.aldebaran.lan/89507
Reviewed-by: vincent.palancher <f8ff75e1c61314c499fafa8de0d9e004e87e66b0@external.softbankrobotics.com>
Reviewed-by: jlamotte <70353e7b0c7d18b7fc75605daf0ccba69fcd3222@aldebaran.com>
Reviewed-by: jmonnon <8898eaf233516e520f996a244ca8a12d20f948b1@aldebaran.com>
Tested-by: vincent.palancher <f8ff75e1c61314c499fafa8de0d9e004e87e66b0@external.softbankrobotics.com>

aldebaran/libqi,aldebaran/libqi,aldebaran/libqi