Use license classifiers rather than the license field.

The license field has a 'free' format, while the classifiers are unique
identifiers, similar to SPDX identifiers. In the documentation, we
should therefore showcase the use of classifiers.

These sections of the documentation were never written, and refer to deprecated functionality anyway, so they can be removed.

Disallow parent path traversal in resource paths, part 1 (deprecation)