Remove some non-logger output and fix ID list sync logging

[doughsay]

Removes two println! lines:

• in statsig-elixir/native/statsig_elixir/src/statsig_nfi.rs - I think this was likely accidentally left in and not meant to be there.
• in statsig-rust/src/output_logger.rs - This is the only instance of printed output not going through the configurable logger. We can't disable this with the output_log_level option, and therefore it pollutes our output when running automated tests. I'd prefer this is removed, but if there's another way to solve the problem, please let me know.

Updated statsig_http_id_lists_adapter.rs to act more like statsig_http_specs_adapter.rs

• Use log_e! instead of log_w!
• Don't log when DisableNetworkOn