The info/hint category of dart analyzer diagnostics is being removed: dart-lang/sdk#50796

As part of that effort, one of the "info" diagnostics that we use in our unit tests (missing_return) was changed to a "warning" https://dart-review.googlesource.com/c/sdk/+/282164. This broke the Engine -> Framework roller when the dart sdk change bubbled up to the framework: https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8789134064052154849/+/u/run_test.dart_for_tool_integration_tests_shard_and_subshard_3_4/test_stdout

I am looking to temporarily revert this change in the dart sdk to unblock the rollers, but it will eventually need to reland. We could use a different info diagnostic to check these tests, but since this entire category of diagnostics is going away, we probably just need to remove some unit tests entirely, and possibly modify the tool to remove command line flags associated with info style diagnostics since they will no longer exist.