The current javadoc generation first creates the coredocs Javadoc, and after that all the remaining javadoc instances.

This dependency is not really needed, all that is required is that the remaining javadoc instances gets a proper pointer to a package-list file for coredocs. Fixing that will allow them to run in parallel with the coredoc generation.

In addition to this performance fix, I've also cleaned up the (now unnecessary) logic of storing the javadoc command line in .options/.packages files.