RFR: 8232438: Remove ?is-external=true from external links

[Hannes Wallnöfer]

Please review:

JBS: https://bugs.openjdk.java.net/browse/JDK-8232438
Webrev: http://cr.openjdk.java.net/~hannesw/8232438/webrev.00/

The is-external=true query was the only use of query functionality in DocLink, so I removed support for query strings in DocLink. The rest of the patch consists of removing the query string from test fixtures.

Thanks,
Hannes