Revert 233630 "[Sync] Add dump/import functionality to sync's ab..."

> [Sync] Add dump/import functionality to sync's about tab
> 
> A dump button, that by default excludes identifiable info, along with an import
> button capable of consuming the dumped data, are now present on the
> chrome://sync-internals about tab.
> 
> BUG=309112
> R=rlarocque@chromium.org
> TBR=rkc@chromium.org
> 
> Review URL: https://codereview.chromium.org/60693002

TBR=zea@chromium.org

Review URL: https://codereview.chromium.org/59413004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233645 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233645