Update/remove 65-bit tests for Dart2

[kevmoo]

Reproduce:

pub run test test/tokenizer_test.dart -N '65-bit'
works on Dart stable
fails on Dart 2.0.0-dev.15

DART_VM_OPTIONS='--no_limit_ints_to_64_bits' pub run test test/tokenizer_test.dart -N '65-bit'
Works on Dart 2.0.0-dev.15

See failures:
Before: https://travis-ci.org/dart-lang/html/jobs/326615035
After: https://travis-ci.org/dart-lang/html/jobs/327414723