Remove the hack for print preview scrolling added in https://codereview.chromium.org/912433002

The bug (crbug.com/455439) has now been fixed.

BUG=455430

Review URL: https://codereview.chromium.org/1015523004

Cr-Commit-Position: refs/heads/master@{#321236}

chrome/browser/resources/print_preview/previewarea/margin_control.css

@@ -34,10 +34,6 @@
   border-color: rgb(64, 128, 250);
   border-style: dashed;
   border-width: 1px;
-  /* TODO(raymes): This is a hack needed to force the margins onto separate
-   * layers to work around crbug.com/455439. We can remove this when it's fixed.
-   */
-  will-change: transform;
 }
 
 #preview-area .margin-control-disabled .margin-control-line  {