Resolve "Extract EE specific files/lines for lib/gitlab/auth"

CE MR: https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/19037

What does this MR do?

This extracts EE-specific code from lib/gitlab/auth/ to ee/.

• 39596a29 2018-05-18 | Extract EE-specific lines to EE::Gitlab::Auth::UserAuthFinders [Rémy Coutable]
• b3c993a7 2018-05-18 | Extract EE-specific lines to EE::Gitlab::Auth::Saml::Config [Rémy Coutable]
• 58648560 2018-05-18 | Extract EE-specific lines to EE::Gitlab::Auth::LDAP::Config [Rémy Coutable]
• 7b8a3306 2018-05-18 | Remove EE-specific comment from EE::Gitlab::Auth::LDAP::Person [Rémy Coutable]
• 12d09c5f 2018-05-18 | Extract EE-specific lines to EE::Gitlab::Auth::Saml::User [Rémy Coutable]
• 018c3d2a 2018-05-18 | Extract EE-specific lines to EE::Gitlab::Auth::LDAP::Access [Rémy Coutable]

Are there points in the code the reviewer needs to double check?

I will add diff notes.

Does this MR meet the acceptance criteria?

• [-] Changelog entry added, if necessary
• [-] Documentation created/updated
• [-] API support added
• [-] Tests added for this feature/bug
• Conform by the code review guidelines
  • Has been reviewed by a Backend maintainer
• EE specific content should be in the top level /ee folder
• Conform by the merge request performance guides
• Conform by the style guides
• If you have multiple commits, please combine them into a few logically organized commits by squashing them
• Internationalization required/considered
• If paid feature, have we considered GitLab.com plan and how it works for groups and is there a design for promoting it to users who aren't on the correct plan
• End-to-end tests pass (package-qa manual pipeline job)

What are the relevant issue numbers?

Closes #5913 (closed)