Remove outdated and superfluous settings from JVM options file

Started as getting rid of -XX:ParNewGC, as that yields a warning in Java 8, and morphed into a general cleanup.

Get rid of all the noisy comments that weren't really helpful and the completely unused sections. The end result is now the *nix and Windows versions are essentially the same and the packaged versions just have more (JMX, debugging) commented out.