RFR (S): 8056043: G1 does not uncommit within the heap after JDK-8038423

[Thomas Schatzl]

Hi all,

 can I have reviews for the following change that removes some code that
has accidentally been left in when splitting off refactoring changes
JDK-8054818 from (the original) JDK-8038423?

Basically, to implement JDK-8054818 there has been need to retain the
old commit/uncommit strategy to only allow uncommit at the end of the
heap. One check that guaranteed that has been left in.

This change removes that one. It also reenables a jtreg test that checks
that, which had been disabled until now because of the functionality
lacking.

CR:
https://bugs.openjdk.java.net/browse/JDK-8056043
Webrev:
http://cr.openjdk.java.net/~tschatzl/8056043/webrev/
Testing:
jprt, vm.gc testlist run, gcbasher for an hour, test case

Thanks,
  Thomas