[lworld] RFR: 8373608: [lworld] Remove ObjBufferAllocator

[Stefan Johansson]

On Mon, 15 Dec 2025 08:38:09 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

>> Please review this change to remove `ObjBufferAllocator` since the impementation now is identical to `ObjAllocator`. 
>> 
>> **Summary**
>> This was not the case when ObjBufferAllocator was first introduced. Back then it skipped clearing the memory and just called oopDesc::set_klass_gap(mem, 0). This is no longer the case after [JDK-8350630](https://bugs.openjdk.org/browse/JDK-8350630) in which `ObjBufferAllocator` was changed to also clear the memory. The previous optimization is likely not needed and we should streamline the code to always use `ObjAllocator`.
>> 
>> **Testing**
>> * mach5 tier1-3 (ongoing)
>
> Looks good.

Thanks for the review @stefank

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PR Comment: https://git.openjdk.org/valhalla/pull/1794#issuecomment-3664901498