Remove `services: true` from spec/services/ci/pipeline_trigger_service_spec.rb

What does this MR do?

This MR removes services: true from spec/services/ci/pipeline_trigger_service_spec.rb.

The code is unnecessary as @godfat mentioned at https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2557#note_36406737.

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

Why was this MR needed?

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

• https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/2557#note_36406737

/cc @godfat