DeviceList: Do not emit adapter-changed twice

Thanks @MikuChan03 for pointing out the problem and the solution.

blueman/gui/DeviceList.py

@@ -244,7 +244,6 @@ def set_adapter(self, adapter=None):
             try:
                 self.Adapter = self.manager.get_adapter(adapter)
                 self.__adapter_path = self.Adapter.get_object_path()
-                self.emit("adapter-changed", self.__adapter_path)
             except bluez.errors.DBusNoSuchAdapterError:
                 logging.warning('Failed to set adapter, trying first available.')
                 self.set_adapter(None)