sip_utils: Nuke sip_utils::register_thread()

src/ice_transport.cpp

src/jamidht/channeled_transport.cpp

src/jamidht/jamiaccount.cpp

src/sip/sdp.cpp

src/sip/sip_utils.cpp

src/sip/sip_utils.h

src/sip/sipaccount.cpp

src/sip/sipvoiplink.cpp