Observatory is being deprecated for Dart 3.0 so it should no longer be
referenced in tooling messaging / flags.

See https://github.com/dart-lang/sdk/issues/50233

* Updated skipped tests for flutter_tools.

* Turned the flaky overall_experience test off as it was still failing on CI.

* opt out the flutter tool

* oops EOF

* fix import

* Update tool_backend.dart

* Update daemon_client.dart

* fix more

This reverts commit 5e0aa8b9.

This reverts commit 4fde217d.