Summary: Enable shrinking within the heap by removing some code added for JDK-8054818. Enable the test case that checks that again too.
Reviewed-by: jwilhelm, jmasa

8037925: CMM Testing: an allocated humongous object at the end of the heap should not prevents shrinking the heap
Summary: New test added.
Reviewed-by: ehelin, tschatzl, jwilhelm
Contributed-by: andrey.x.zakharov@oracle.com