Remove old illustrations

Purpose

Remove outdated unused illustrations.

pipeline_schedules_callout -> gitlab!131925 (merged)

search-timeout-md -> gitlab!132979 (merged)

chat-bubble-sm, illustration-congratulation-purchase -> gitlab!138067 (merged)

security-dashboard-empty-state, cycle-analytics-empty-chart -> gitlab!138820 (merged)

epics/roadmap, epics/list -> gitlab!139077 (merged)

canceled-job_empty, illustrations_scheduled-job_countdown, job_not_triggered, pending_job_empty, skipped-job_empty -> gitlab!139644 (merged)

project-run-CICD-pipelines-sm -> gitlab!139256 (merged)

autodevops -> gitlab!141707 (merged)

ondemand-scan-empty — no mentions

Checklist

For a new icon and/or illustration:

• Link to related design issue:
• If this adds an icon ensure that it follows the new icon checklists.
• If this adds an illustration ensure that it follows the new illustration checklists.

For third-party trademarks:

• If this adds or updates an icon or illustration that includes a third-party trademark, ensure that it follows the process for adding third-party trademarks to GitLab.