Remove duplicates from npm dependencies

What does this MR do?

Removes duplicates from the dependency list. This only covers npm dependencies because over package types should be affected by this issue.

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ee/issues/12162

Test

Forked our test project and run it with DS with this change. You can see dependency list doesn't include any duplicates.

https://gitlab.com/caneldem/js-npm/dependencies

Does this MR meet the acceptance criteria?

• Changelog entry added
• [-] Documentation created/updated for GitLab EE, if necessary
• [-] Documentation created/updated for this project, if necessary
• [-] Documentation reviewed by technical writer or follow-up review issue created
• Tests added for this feature/bug
• [-] Job definition updated, if necessary
• Conforms to the code review guidelines
• Conforms to the Go guidelines
• [-] Security reports checked/validated by reviewer