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

[Stefan Karlsson]

On Fri, 12 Dec 2025 15:28:27 GMT, Stefan Johansson <sjohanss 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.

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Marked as reviewed by stefank (Author).

PR Review: https://git.openjdk.org/valhalla/pull/1794#pullrequestreview-3577030408