Benchmark object deletion and compare to no-batching

[ChrisSchinnerl]

When multiple objects are deleted they are deleted in batches with a dynamic batch size. Since we are no longer pruning slabs in the same db txn we might not need that sort of batching anymore.

We should write a benchmark and then see what works best. Maybe we can simplify the code to not batch or just use a static batch size of 100k objects now.