Delete many duplicate tests in checker_test, mostly INVALID_OVERRIDE
Delete many duplicate tests in checker_test, mostly INVALID_OVERRIDE

* Tests for FIELD_INITIALIZER_OUTSIDE_CONSTRUCTOR exist
* Matching tests for grand interfaces, for fields, getters, setters
* Matching tests for covariant parameters and fields
* Matching tests for mixins

Change-Id: I34bfab70da5323568f7178488b26179f0a6e10ad
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/197580
Reviewed-by: Brian Wilkerson <1f7641b6b14c52b9163524ab8d9aabff80176f21@google.com>
Commit-Queue: Samuel Rawlins <5cf2cac5eec2ad6d0eb2b0f4ff6af9a590ce2bf6@google.com>

dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk,dart-lang/sdk