Remove duplication of Licenses in Dependency List page

Summary

If there are multiple versions of the same dependency, and they share the same license, this license can appear multiple times in the Dependency List.

Steps to reproduce

  1. Find a project with different versions of the same dependency in the project.
  2. Go to Security & Compliance > Dependencies.
  3. Find this dependency.
  4. Observe License field

Example Project

https://gitlab.com/gitlab-org/gitlab-ui/dependencies

What is the current bug behavior?

The same license occurs multiple times in one field.

What is the expected correct behavior?

The license occurs only one time

Relevant logs and/or screenshots

Screenshot_from_2019-09-16_09-30-59

Output of checks

This bug happens on GitLab.com

Possible fixes

Remove duplicates of licenses on parsing step in the backend.