datatransfer: remove path for non swarm conversations

src/libclient/api/conversationmodel.h

src/libclient/api/datatransfermodel.h

src/libclient/callbackshandler.cpp

src/libclient/conversationmodel.cpp

src/libclient/datatransfermodel.cpp

src/libclient/qtwrapper/configurationmanager_wrap.h