shared/async: don't use WEXITED for waitpid()

Follow-up for c26d7837bb

waitpid() doesn't support WEXITED and returns -1 (EINVAL),
which results in the intermediate close process not getting
reaped.

Fixes https://github.com/systemd/systemd/issues/26744#issuecomment-1628240782

src/shared/async.c

@@ -103,10 +103,9 @@ int asynchronous_close(int fd) {
                  *
                  * We usually prefer calling waitid(), but before kernel 4.7 it didn't support __WCLONE while
                  * waitpid() did. Hence let's use waitpid() here, it's good enough for our purposes here. */
-                for (;;) {
-                        if (waitpid(pid, NULL, WEXITED|__WCLONE) >= 0 || errno != EINTR)
+                for (;;)
+                        if (waitpid(pid, NULL, __WCLONE) >= 0 || errno != EINTR)
                                 break;
-                }
         }
 
         return -EBADF; /* return an invalidated fd */