wait/wait02: cleanup

* Delete some useless comments and variables.
* Some cleanup.

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Jan Stancek <jstancek@redhat.com>
wait/wait01.c: Add ECHILD test

Add ECHILD test for wait(2).

Signed-off-by: Zeng Linggang <zenglg.jy@cn.fujitsu.com>
Signed-off-by: Jan Stancek <jstancek@redhat.com>