Follow up issue for sort by licenses on project dependency list (493788)

This is a follow up issue for the following issue: #493788 (closed) as mentioned in the following comment: !170776 (comment 2185160914)

Things to do:

1. Update the docs here https://docs.gitlab.com/ee/user/application_security/dependency_list/index.html#view-project-dependencies where it says You can sort the list instead by component name or packager, so that it mentions sorting by licenses as well.
2. Clean up SORT_FIELDS_PROJECT and SORT_FIELDS_GROUP, since they contain the same value now and we don't need two different constants anymore.