Java Automodel extraction: remove primitives in framework mode

[kaeluka]

This removes some candidates and examples from framework mode, based on feedback from the Java team (see backref).

The suggestion was to drop primitive values from consideration; additionally, as a drive-by, this PR also removes source candidates of methods return values when the method is returning void.

I've asked Tony for a review, as he suggested removing this. The PR is quite short. LMK if you have any questions 👍 🙂

- [x] Remove return-value source endpoints for primitive methods in framework mode
- [x] Remove return-value source candidates for void methods in framework mode
- [x] Remove parameter-source-candidates for primitive parameters in framework mode

[atorralba]

LGTM! I added a couple of comments for your consideration.