PSA: PeerConnectionObserver destructor becoming virtual and public

[Sami Kalliomäki]

Hi,

PeerConnectionObserver used to have a protected non-virtual destructor. With this change, it will have a public virtual destructor. This is done to allow destruction of objects through the interface.

If clients have inherited classes from this interface with virtual destructors, they may wish to mark the destructor as override instead of virtual.

Regards,

Sami Kalliomäki