tor-config-path: finish migration from tor-config

In !2590 (merged) the tor_config::path module was moved to a new tor-config-path library, but there are a few outstanding issues:

1. The tor-config library re-exports CfgPath and CfgPathError from tor-config-path. We should remove this re-export and update all of the code to use their new location.
2. The tor-config library has the "expand-paths" feature which isn't used anymore (it's used by tor-config-path now). We should remove it from tor-config. We might be able to remove a few other dependencies from tor-config now as well.
3. The test_parse test in tor-config-path was commented-out since it depends on the internals of tor-config.

Labeling as "project 141" since I think this crate split is useful for relays too, but maybe an rpc label would be better.