`perform_enqueued_jobs` is a Sidekiq method.
Using this method violates the Dependency inversion principle[0].
This commit replaces `perform_enqueued_jobs` with ActiveJob's abstract
method `perform_enqueued_jobs` in specs.
[0]: https://en.wikipedia.org/wiki/Dependency_inversion_principle
[10.6] Prevent notes on confidential issues from being sent to chat
See merge request gitlab/gitlabhq!2366
# Conflicts:
# app/helpers/services_helper.rb
