Outdated links in Javadoc documentation

The MySQL connector codebase contains Javadoc pointing to the non-existing symbols via the {@link ...} tag. It leads to the following issues from the developer experience standpoint:

1. The codebase is harder to navigate.
2. Some IDEs may report such documentation in a way visually similar to type errors. This causes unnecessary distraction.

The code also contains non-API methods that aren't used anywhere.