RFR: Updated section on Code Conventions.

[mark.reinhold at oracle.com]

2020/6/18 6:10:21 -0700, Andreas Lundblad <github.com+5994243+aioobe at openjdk.java.net>:
> Pull request for adding code conventions.

Thanks for contributing this material, but I don’t think that the
Developers’ Guide is the right place for it.

If we have agreed policies about coding style then we should treat
them as authoritative, normative information.  As such, they’d be
out of place in a Guide that’s meant only to contain tutorials and
suggestions.

- Mark