RFR(S): 8195109: ServiceUtil::visible_oop is not needed anymore

[Chris Plummer]

Hello,

Please review the following:

https://bugs.openjdk.java.net/browse/JDK-8195109
http://cr.openjdk.java.net/~cjplummer/8195109/webrev.00/index.html

The assert I added to make sure this is safe has been in place in 
jdk/jdk for almost 3 weeks with no issues (longer in jdk/hs).

The webrev is missing the copyright update for threadService.hpp. I 
fixed it after noticing that.

Testing is in progress. Running hs tiers 1, 2, and 3, and jdk tiers 1 
and 2. Also making sure all serviceability tests are run.

thanks,

Chris