`run_benchmarks` is referenced in the documentation and the codebase but is not available

The [documentation](https://google.github.io/xls/tools/#benchmark_main) of the `benchmark_main` points to `run_benchmarks`, also `run_benchmarks.py` is mentioned in the [codebase](https://github.com/google/xls/blob/main/xls/tools/benchmark_codegen_main.cc#L33), but the tool seems to be unavailable in the repository. Is this part of the documentation up to date? Is the tool still needed/used somewhere?

If so, would it be possible to update the documentation about it?

CC @proppy