Remove or_options_t dependencies from module config headers

The following inline header functions depend on some members of or_options_t, which is a dependency we don't need:

• options_validate_dirauth_mode()
• options_validate_server_transport()
• options_validate_relay_mode() And the dependency only exists when the relay or dirauth modules are disabled.

Instead, we could put these functions in stub C files, which are only compiled when relay/dirauth mode is disabled.