SRCH-6454 Remove deprecated ClickCounter, searchgov:promote, and AdvancedSearchesConstraint

[luisgmetzger]

Summary

Removes three pieces of deprecated code that depend on i14y / the SearchGov engine, which is no longer in use after Phase 1 completion (SRCH-6428):

• ClickCounter service, ClickCounterJob, ClickMonitorJob, and the weekly cron schedule entry in resque_schedule.yml
• searchgov:promote rake task (manual-only, no longer functional with i14y going away)
• AdvancedSearchesConstraint class (already disconnected from routes.rb; /search/advanced redirects unconditionally)

Also removes orphaned test fixtures and a stale .rubocop_todo.yml exclusion.

14 files changed, 1 insertion, 872 deletions.

What is NOT removed

• The click_count field in OpenSearch (still used for relevancy ranking; spider handles it differently)
• I14yDocument.promote model method (will be cleaned up when i14y is fully decommissioned)
• searchgov:crawl rake task (separate concern)

Deploy notes

• Deploy on a weekday (not Sunday) to avoid race with the now-removed ClickMonitorJob cron
• Before deploy, verify no pending ClickCounterJob entries in the Resque searchgov queue
• Monitor for NameError on removed constants for 48 hours post-deploy

Test plan

• Grep confirms zero remaining references to ClickCounter, ClickMonitorJob, ClickCounterJob, searchgov:promote, AdvancedSearchesConstraint
• CI test suite passes
• rake -T searchgov shows only searchgov:crawl
• /search/advanced redirect still works
• config/resque_schedule.yml only has SitemapMonitorJob