Remove old and unused test file (#589)
Remove old and unused test file (#589)

This file was needed in older versions of Dart. It's currently not used,
and the tests do not pass when run, probably because of the static
variable in protoc_plugin/lib/src/code_generator.dart:23.
dart-lang/dart-protobuf,google/protobuf.dart,dart-lang/protobuf,dart-lang/protobuf,dart-lang/dart-protobuf,google/protobuf.dart,google/protobuf.dart,dart-lang/protobuf,dart-lang/dart-protobuf