Remove unnecessary step from shapes.drawAll()

* Removed call to `.remove()` in `shapes.drawAll()`, since `.remove()`
  is also call in `shapes.draw()`.

* No new test failed after this change.

src/components/shapes/index.js

@@ -89,7 +89,6 @@ function linearToData(ax) { return ax.type === 'category' ? ax.l2c : ax.l2d; }
 
 shapes.drawAll = function(gd) {
     var fullLayout = gd._fullLayout;
-    fullLayout._shapelayer.selectAll('path').remove();
     for(var i = 0; i < fullLayout.shapes.length; i++) {
         shapes.draw(gd, i);
     }