Remove unused import from _tests/tool/build.dart.
Remove unused import from _tests/tool/build.dart.

PiperOrigin-RevId: 173288694

chalin/angular2,chalin/angular2,kevmoo/angular,matanlurey/angular,matanlurey/angular,angulardart/angular,kevmoo/angular,matanlurey/angular,chalin/angular2,kevmoo/angular,angulardart/angular,angulardart/angular