Remove `lib/tunnel.c`, it is no longer referenced from anywhere.
Remove `lib/tunnel.c`, it is no longer referenced from anywhere.

devnexen/h2o,yannick/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,yannick/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,yannick/h2o,yannick/h2o,h2o/h2o,devnexen/h2o,h2o/h2o,devnexen/h2o,devnexen/h2o,h2o/h2o,h2o/h2o,yannick/h2o,yannick/h2o,devnexen/h2o,yannick/h2o,devnexen/h2o,h2o/h2o