Since `263863@main` we always know the test fonts directory path and `FONTS_CONF_DIR` is not needed anymore.
Pull request: https://github.com/WebKit/WebKit/pull/13748
Committed 263967@main (dc42c0d5cf96): <https://commits.webkit.org/263967@main> Reviewed commits have been landed. Closing PR #13748 and removing active labels.