[ENG-6223] chore: remove 'old' institution dashboard stuff

[aaxelb]

Purpose

clean up after the last institution dashboard project, now that the dust has settled and its feature flag is permanently on

Changes

• remove feature flag INSTITUTIONAL_DASHBOARD_2024 and all code deadened by it
  • delete "old" views and serializers for institution summary and institution user
  • rename corresponding "new" views and serializers to remove "new"
  • delete osf.metrics.InstitutionProjectCounts (replaced by osf.metrics.reports.InstitutionMonthlySummaryReport)
  • delete osf.metrics.UserInstitutionProjectCounts (replaced by osf.metrics.reports.InstitutionalUserReport)
• update institution-departments view to get department names and counts from InstitutionalUserReport (instead of UserInstitutionProjectCounts)
  • because the data comes from an aggregation, simplify by always returning the full list (no pagination)
  • allows removing InstitutionImpactList, MockQueryset, api.institutions.renderers

post-deployment notes

after this, should be safe to delete metrics indexes osf_institutionprojectcounts_* and osf_userinstitutionprojectcounts_*

QA Notes

Please make verification statements inspired by your code and what your code touches.

• Verify institutional dashboard summary and users tabs still work as expected
• Verify institutional dashboard department lists still work as expected

What are the areas of risk?

• departments names on the institutional dashboard

Any concerns/considerations/questions that development raised?

Documentation

Side Effects

Ticket

ENG-6223

[Johnetordoff]

Excellent work, I couldn't have done it better myself. 🥇