RFR: 8223699: cleanup perfMemory_aix.cpp O_NOFOLLOW coding on aix

[Baesken, Matthias]

Hello, please review  this AIX specific cleanup.

In perfMemory_aix.cpp we still have O_NOFOLLOW related fallback coding for AIX version < 7.X.
This is no longer needed, because we do not support any more AIX versions < 7.X in coming jdk13, so cleanup is possible.


Bug/webrev :

https://bugs.openjdk.java.net/browse/JDK-8223699

http://cr.openjdk.java.net/~mbaesken/webrevs/8223699.1/


Thanks, Matthias