The impementation of `ObjBufferAllocator` is identical to `ObjAllocator`. 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 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`.