RFR 8167227: Simplify the JDK 9 API-specification overview page (docs only)

[mark.reinhold at oracle.com]

http://cr.openjdk.java.net/~mr/rev/8182408/
https://bugs.openjdk.java.net/browse/JDK-8182408

This is a follow-on to Magnus's changes for 8175824.

Oracle's legal department has recently advised that the liberal use of
trademark symbols on the API-specification overview page is not required.
We should, rather, just include a registered-trademark symbol (®)
after the first prominent instance of "Java". The warnings about the
provisional nature of the API can also be simplified.

The webrev page contains links to example Javadoc output for different
variants: GA vs. ad-hoc, and SE + JDK + FX vs. SE + JDK vs. just SE.

Current output, for reference:
http://download.java.net/java/jdk9/docs/api/overview-summary.html

Thanks,
- Mark