Remove the unused FKs referencing ci_pipelines

What does this MR do and why?

Remove the unused FKs referencing ci_pipelines

• p_ci_builds.fk_87f4cefcda (see the new one p_ci_builds.fk_87f4cefcda_p at https://console.postgres.ai/gitlab/gitlab-production-ci/sessions/30726/commands/95533)
• ci_pipelines.fk_262d4c2d19 (see the new one ci_pipelines.fk_262d4c2d19_p at https://console.postgres.ai/gitlab/gitlab-production-ci/sessions/30726/commands/95536)
• ci_daily_build_group_report_results.fk_rails_ee072d13b3 (see the new one ci_daily_build_group_report_results.fk_rails_ee072d13b3_p at https://console.postgres.ai/gitlab/gitlab-production-ci/sessions/30726/commands/95538)

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Related to #436529 (closed) #436531 (closed)