(jdeprscan) update release and version logic in jdeprscan

Need to determine a mechanism for updating jdeprscan's supported -release values in lockstep with those of javac. If there is a compiler API that returns the supported versions, jdeprscan should use it. Otherwise, the following will need to be updated manually.

In Main.java:

    final Set<String> releasesWithoutForRemoval = Set.of("6", "7", "8");
    final Set<String> releasesWithForRemoval = Set.of("9");

The new release should be added to releasesWithForRemoval and the obsoleted release dropped from releasesWithoutForRemoval.

In LoadProc.java and TraverseProc.java, update @SupportedSourceVersion(RELEASE_9).

The resources/jdeprscan.properties file needs to be modified to update the usage message.

The readme.md file also needs to be updated. (But this is probably duplicate information from what's in the online reference manual documentation, so maybe this file should simply be removed.)