Remove all static analysis warnings for different parameter override value

[srawlins]

For dart-lang/sdk#49112, we will stop reporting STATIC_WARNING.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_POSITIONAL and STATIC_WARNING.INVALID_OVERRIDE_DIFFERENT_DEFAULT_VALUES_NAMED altogether. These should be removed from pre-null safety co19 tests (co19_2 directory in sdk repo).

See failures here when analyzer stops reporting these: https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket/8801563216397856865/+/u/test_results/new_test_failures__logs_