Remove deprecated members from ErrorCode.
Remove deprecated members from ErrorCode.

These existed as an effort to avoid causing breaking changes in the
analyzer package, but it turns out that the analyzer package already has
breaking changes in progress, so there is no benefit.

R=brianwilkerson@google.com

Review URL: https://codereview.chromium.org/2491593003 .

dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-archive/dart-sdk,dart-lang/sdk,dartino/dart-sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-archive/dart-sdk,dartino/dart-sdk,dart-lang/sdk,dart-lang/sdk,dartino/dart-sdk