Revert of Fix selection of label having control element. (https://codereview.chromium.org/258933006/)

Reason for revert:
Causes bug 370859

BUG=148912,370859
TBR=keishi

Original issue's description:
> Fix selection of label having control element.
>
> Any click event on label goes to its control element. So, if
> we tried to select the text inside label by dragging the mouse
> or by double clicking on the text, it went to its control
> element. This patch checks whether there is selection or not,
> after the click is happened. If there is selection then do
> nothing else continue.
>
> New Layout test added:
>  fast/forms/label/label-selection.html
>
> BUG=148912
>
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=173310

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=174193

Review URL: https://codereview.chromium.org/290153002

git-svn-id: svn://svn.chromium.org/blink/trunk@174210 bbb929c8-8fbe-4397-9dbb-9b2b20218538