Remove duplicate copy of animation/curves.dart in fn widgets

sky/examples/fn/widgets/animationgenerator.dart

 part of widgets;
 
 class FrameGenerator {
 
   Function onDone;
   StreamController _controller;
 
   Stream<double> get onTick => _controller.stream;
 
   int _animationId = 0;
@@ skipping 63 matching lines @@
     .map((t) =>  begin + (end - begin) * curve.transform(t));
   }
 
   bool _checkForCompletion(double t) {
     if (_done)
       return false;
     _done = t >= 1;
     return true;
   }
 }
-
-double _evaluateCubic(double a, double b, double m) {
-  // TODO(abarth): Would Math.pow be faster?
-  return 3 * a * (1 - m) * (1 - m) * m + 3 * b * (1 - m) * m * m + m * m * m;
-}
-
-const double _kCubicErrorBound = 0.001;
-
-abstract class Curve {
-  double transform(double t);
-}
-
-class Linear implements Curve {
-  const Linear();
-
-  double transform(double t) {
-    return t;
-  }
-}
-
-class Cubic implements Curve {
-  final double a;
-  final double b;
-  final double c;
-  final double d;
-
-  const Cubic(this.a, this.b, this.c, this.d);
-
-  double transform(double t) {
-    if (t == 0.0 || t == 1.0)
-      return t;
-
-    double start = 0.0;
-    double end = 1.0;
-    while (true) {
-      double midpoint = (start + end) / 2;
-      double estimate = _evaluateCubic(a, c, midpoint);
-
-      if ((t - estimate).abs() < _kCubicErrorBound)
-        return _evaluateCubic(b, d, midpoint);
-
-      if (estimate < t)
-        start = midpoint;
-      else
-        end = midpoint;
-    }
-  }
-}
-
-const Linear linear = const Linear();
-const Cubic ease = const Cubic(0.25, 0.1, 0.25, 1.0);
-const Cubic easeIn = const Cubic(0.42, 0.0, 1.0, 1.0);
-const Cubic easeOut = const Cubic(0.0, 0.0, 0.58, 1.0);
-const Cubic easeInOut = const Cubic(0.42, 0.0, 0.58, 1.0);