RFR(m): 8223306: Remove threads linked list (use ThreadsList's array in SA)

[Robbin Ehn]

Hi, please review.

Old threads linked list remove and updated SA to use ThreadsList array instead.

Issue:
https://bugs.openjdk.java.net/browse/JDK-8223306
Webrev:
http://cr.openjdk.java.net/~rehn/8223306/webrev/

Passes t1-3 (which includes SA tests).

Thanks, Robbin