[reverted] writing CHANGED to state on every move

Summary: @jverkoey had requested this in http://codereview.cc/D3085, but had forgotten that `state` and `drag` are separate streams in this implementation, so `state` only needs to be written to when it has changed.

Reviewers: O2 Material Motion, O3 Material JavaScript platform reviewers, #material_motion, featherless

Reviewed By: O2 Material Motion, #material_motion, featherless

Tags: #material_motion

Differential Revision: http://codereview.cc/D3118

packages/core/src/systems/dragSystem.ts

@@ -81,12 +81,6 @@ export function dragSystem({
                     state.write(GestureRecognitionState.CHANGED);
                     break;
 
-                  case GestureRecognitionState.CHANGED:
-                    if (!atRest) {
-                      state.write(GestureRecognitionState.CHANGED);
-                    }
-                    break;
-
                   default:break;
                 }