dirauth: Disable dirauth config when the module is disabled

src/core/include.am

src/feature/dirauth/dirauth_config.c

src/feature/dirauth/dirauth_config.h

src/test/conf_examples/bridgeauth_1/error_no_dirauth

src/test/conf_examples/bridgeauth_1/error_no_dirauth_relay

src/test/conf_examples/bridgeauth_1/expected_no_dirauth

...test/conf_examples/bridgeauth_1/expected_no_dirauth_relay

src/test/conf_examples/dirauth_1/error_no_dirauth

src/test/conf_examples/dirauth_1/error_no_dirauth_relay

src/test/conf_examples/dirauth_1/expected_no_dirauth

src/test/conf_examples/dirauth_1/expected_no_dirauth_relay