Delete legacy analytics.

[kenzieschmoll]

Deletes the legacy analytics so that we no longer send analytics to two separate GA4 ids. Changes covered by existing tests.

Fixes #9765.

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[gemini-code-assist]

Code Review

This pull request removes legacy Google Analytics (GA) logic across several packages and refactors the web analytics implementation to use a Dart-based event system, replacing previous JS interop calls. Key changes include the removal of legacy server endpoints, the deletion of gtags.dart and devtools_analytics.js, and the introduction of type-safe enums for analytics parameters. Review feedback highlighted critical logical issues in _analytics_web.dart, specifically regarding the misuse of immutable string methods, a potential out-of-bounds error during list iteration, and the use of unnormalized platform strings.