Fix the number of clients spawned by Launcher (#349)

libafl/src/bolts/launcher.rs

@@ -222,7 +222,6 @@ where
                 //spawn clients
                 for (id, _) in core_ids.iter().enumerate().take(num_cores) {
                     if self.cores.iter().any(|&x| x == id) {
-                        for id in 0..num_cores {
                         let stdio = if self.stdout_file.is_some() {
                             Stdio::inherit()
                         } else {
@@ -236,7 +235,6 @@ where
                         }
                     }
                 }
-                }
 
                 handles
             }