Delete old unused javadoc package

We somehow have an internal unused package for javadoc, see https://github.com/INRIA/spoon/tree/master/src/main/java/spoon/javadoc/internal. Given we have a new javadoc parser from @I-Al-Istannen we can clean up this for java 17 branch. WDYT?

Start by inspecting src/main/java/spoon/javadoc/internal and checking whether the package is still referenced, especially in the Java 17 branch. The work is done when the old unused package is removed without breaking the new javadoc parser or the project build.

Written by the indexing model from the issue text.