[EE] Remove explicit `require` calls, and use `require_dependency` when needed
EE version of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/9899.
What does this MR do?
This removes some unnecessary require
and use require_dependency
instead of require
when necessary (or when I was unsure the require
was needed).
See http://guides.rubyonrails.org/autoloading_and_reloading_constants.html#require-dependency for reference.
Related to #29389 (closed) /cc @nick.thomas