RCON: remove redundant sleep

this dates back to the days where PM used to kill threads to stop them. Today we're more civilized and ask it to stop nicely, so this isn't necessary anymore.

src/pocketmine/network/rcon/RCON.php

@@ -85,7 +85,6 @@ class RCON{
 	public function stop(){
 		$this->instance->close();
 		socket_write($this->ipcMainSocket, "\x00"); //make select() return
-		Server::microSleep(50000);
 		$this->instance->quit();
 
 		@socket_close($this->socket);