4870. [test] Update included ATF library to atf-0.21 preserving

the ATF tool. [RT #46967]

(cherry picked from commit 23d77c8747)

unit/atf-src/test-programs/cpp_helpers.cpp

@@ -1,6 +1,3 @@
-//
-// Automated Testing Framework (atf)
-//
 // Copyright (c) 2007 The NetBSD Foundation, Inc.
 // All rights reserved.
 //
@@ -25,7 +22,6 @@
 // IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
 // OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 // IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
-//
 
 extern "C" {
 #include <signal.h>