update to rust 1.58.1

[pchickey]

Update to rust 1.58.1, and fix some new warnings:

• benchmarks: delete inline(never) which is apparently unused
• with_ffi_arcs: Arc::into_raw now requires us to explicitly discard the result, which was the intention of the code anyway
• objdump: some of the struct fields were never read, who cares, mark the whole file allow(dead_code) because its heading to the bin anyway