RFR: 8297766: Remove UseMallocOnly development option

[Thomas Stuefe]

On Thu, 1 Dec 2022 15:37:56 GMT, Afshin Zafari <duke at openjdk.org> wrote:

> ### Description
> The UseMallocOnly development option was originally used to detect memory stomping bugs with Arena allocations when the JVM was first in development.
> 
> The option has had a few bugs and is not in general use. There are ideas to add another way of Arena canary checking.
> 
> ### Patch:
> All occurrences of UseMallocOnly are removed.
> 
> ### Tests:
> Local, gTests: resourceArea and Arena
> Mach5: tier1-5

Good riddance :-)

I think `HandleArea` can be simplified too. It does a lot of gymnastics to work around the UseMallocOnly mode.

I believe you can scratch `HandleArea::real_allocate_handle()` and redirect `HandleArea::allocate_handle()` to directly call `Arena::Amalloc`. Have not tested though.

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Changes requested by stuefe (Reviewer).

PR: https://git.openjdk.org/jdk/pull/11456