6993732: Remove the HPI

[Alan Bateman]

The HPI is left over from bygone years where we had a portability layer 
and needed to support green and native threading models. Some of the 
code has not been used or maintained since the transition to HotSpot 
back in jdk1.3. As of jdk7-b123, the HPI library (libhpi.so/hpi.dll) 
isn't loaded and it's finally time to wield the axe and remove this old 
code. The webrev with the changes is here:
   http://cr.openjdk.java.net/~alanb/6993732/webrev/

Thanks,

Alan.