Update Java runtime examples

[thesurlydev]

Now that Java is a first class runtime in up the examples should be simplified/updated.

[kaihendry]

I'm unable to get https://github.com/apex/up-examples/tree/master/oss/java-maven-spark nor https://github.com/apex/up-examples/tree/master/oss/java-maven-springboot working. Log reports sh: java: command not found

Guess the Node.js 10.x runtime doesn't have java installed?

And Java 11 (Corretto) doesn't have nodejs... oh dear.

[tj]

Yeah AWS removed Python as well I think :( and with the way they chose to do layers I can't add the proxy to each Lambda runtime, so it more or less only works with Go & JS at the moment. If they exposed the runtimes as ARNs for use with layers it would be fixable but I think we're out of luck for now