Hello, please review this small AIX related cleanup change .

When recently looking into the  os_perf coding ,  I noticed  that we try to  read   (on AIX)   cpu ticks related data from /proc/stat .

However this will most likely fail, on the AIX machines  I checked  there is a  /proc  but  no  /proc/stat  .

(probably  the AIX coding has been taken over from linux)

The change cleans up  the coding  in  os_perf_aix.cpp  .

( there might be other ways to get the CPU ticks related info on AIX  e.g. by  using libperfstat or by using what  <sys/procfs.h>

has to offer, see  https://www.ibm.com/support/knowledgecenter/en/ssw_aix_71/com.ibm.aix.files/proc.htm    ,  but  this  should be  checked  and maybe  added

  with another change in case someone is interested )

Bug/webrev :

https://bugs.openjdk.java.net/browse/JDK-8221915

http://cr.openjdk.java.net/~mbaesken/webrevs/8221915.0/

Thanks, Matthias