RFR: JDK-8191204 Post-consolidation cleaning up of the build system

[Magnus Ihse Bursie]

I think this is the last round of the post-consolidation cleaning up of 
the build system. I'm removing some now-redundant checks, aligning to 
more common calling practice, and speeding up the hg status check (which 
was becoming more urgent as the repo grow in size).

Bug: https://bugs.openjdk.java.net/browse/JDK-8191204
WebRev: 
http://cr.openjdk.java.net/~ihse/JDK-8191204-post-consolidation-cleanup/webrev.01

/Magnus