chore(insights): Remove unused dashboard migration feature flags (#110044)

## Summary

Removes 13 feature flags from `temporary.py` that are no longer
referenced after the frontend consolidation in #109967. These flags were
for individual insights dashboard platform migrations that have been
consolidated into `useHasPlatformizedInsights`.

Removed flags:
- `performance-session-health-dashboard-migration`
- `insights-queries-dashboard-migration`
- `insights-http-dashboard-migration`
- `insights-backend-overview-dashboard-migration`
- `insights-mobile-vitals-dashboard-migration`
- `insights-mobile-session-health-dashboard-migration`
- `insights-web-vitals-dashboard-migration`
- `insights-frontend-overview-dashboard-migration`
- `insights-queue-dashboard-migration`
- `insights-cache-dashboard-migration`
- `insights-frontend-assets-dashboard-migration`
- `insights-nextjs-frontend-overview-dashboard-migration`
- `insights-laravel-overview-dashboard-migration`

Confirmed no remaining usages in the codebase (only changelog references
in `CHANGES`).

Author: DominikB2014

src/sentry/features/temporary.py

@@ -221,32 +221,6 @@ def register_temporary_features(manager: FeatureManager) -> None:
     manager.add("organizations:performance-queries-mongodb-extraction", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable removing the fallback for metrics compatibility
     manager.add("organizations:performance-remove-metrics-compatibility-fallback", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable session health overview to dashboard platform migration
-    manager.add("organizations:performance-session-health-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable queries module dashboard on dashboards platform
-    manager.add("organizations:insights-queries-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable http module dashboard on dashboards platform
-    manager.add("organizations:insights-http-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable backend overview dashboard on dashboards platform
-    manager.add("organizations:insights-backend-overview-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable Mobile Vitals Insights module on dashboards platform
-    manager.add("organizations:insights-mobile-vitals-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable Mobile Session Health module on dashboards platform
-    manager.add("organizations:insights-mobile-session-health-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable web vitals module dashboard on dashboards platform
-    manager.add("organizations:insights-web-vitals-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable frontend overview dashboard on dashboards platform
-    manager.add("organizations:insights-frontend-overview-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable queue dashboard on dashboards platform
-    manager.add("organizations:insights-queue-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable cache dashboard on dashboards platform
-    manager.add("organizations:insights-cache-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable frontend assets dashboard on dashboards platform
-    manager.add("organizations:insights-frontend-assets-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable Next.js frontend overview dashboard on dashboards platform
-    manager.add("organizations:insights-nextjs-frontend-overview-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
-    # Enable Laravel overview dashboard on dashboards platform
-    manager.add("organizations:insights-laravel-overview-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable AI and MCP module dashboards on dashboards platform
     manager.add("organizations:insights-ai-and-mcp-dashboard-migration", OrganizationFeature, FeatureHandlerStrategy.FLAGPOLE, api_expose=True)
     # Enable all registered prebuilt dashboards to be synced to the database