Minor cleanup in newton

packages/newton/lib/src/scroll_simulation.dart

@@ -45,7 +45,7 @@ class ScrollSimulation extends SimulationGroup {
     if (_spring == null && (position > _trailingExtent || position < _leadingExtent))
       return false;
 
-    /// This simulation can only step forward.
+    // This simulation can only step forward.
     if (!_isSpringing) {
       if (position > _trailingExtent) {
         _isSpringing = true;

packages/newton/lib/src/simulation.dart

@@ -14,7 +14,7 @@ abstract class Simulation {
   double x(double time);
 
   /// The current velocity of the object in the simulation
-  double dx(double time); // TODO(ianh): remove this; see https://github.com/flutter/flutter/issues/2092
+  double dx(double time);
 
   /// Returns if the simulation is done at a given time
   bool isDone(double time);