rustjail: fix unit test test_process

test_process has a assertion that waitpid(-1) will fail
because there is no child process in most cases.

But if there is any child process forked by other unit test,
the test test_process will fail.

Because waitpid(-1) will wait for any child process including the
process created by other unit tests.

Signed-off-by: Tim Zhang <tim@hyper.sh>

src/agent/rustjail/src/process.rs

@@ -253,7 +253,6 @@ mod tests {
 
         // -1 by default
         assert_eq!(process.pid, -1);
-        assert!(process.wait().is_err());
         // signal to every process in the process
         // group of the calling process.
         process.pid = 0;