RFR: 8230398: Remove NULL checks before FREE_C_HEAP_ARRAY

[Kim Barrett]

> On Sep 10, 2019, at 9:39 AM, Leo Korinth <leo.korinth at oracle.com> wrote:
> 
> I will remove NULL assignments of fields in destructors and keep them otherwise.
> 
> I will also add a comment (// handles NULL pointers) to FreeHeap and os::free to not only describe behaviour, but also to establish a contract.
> 
> Also fixed indentation miss in os_perf_windows.cpp
> 
> Incremental:
> http://cr.openjdk.java.net/~lkorinth/8230398/00_01
> 
> Full:
> http://cr.openjdk.java.net/~lkorinth/8230398/01
> 
> 
> running tests...

Looks good.