chg: do not write pidfile Current pidfile logic will only keep the pid of the newest server, which is not very useful if we want to kill all servers, and will become outdated if the server auto exits after being idle for too long. Besides, the server-side pidfile writing logic runs before chgserver gets confighash so it's not trivial to append confighash to pidfile basename like we did for socket file. This patch removes --pidfile from the command starting chgserver and switches to an alternative way (unlink socket file) to stop the server.