Remove SVGGraphicsElement::getStrokeBBox()

The world was not ready for getStrokeBBox(). This API is (correctly)
being removed from SVG2[1] and replaced with a dictionary
argument on the getBBox() function.

This patch reverts r160684[2] which implemented getStrokeBBox() too soon.

[1] http://lists.w3.org/Archives/Public/www-svg/2013Jan/0057.html
[2] http://src.chromium.org/viewvc/blink?view=rev&rev=160684

BUG=280423

Review URL: https://codereview.chromium.org/153553003

git-svn-id: svn://svn.chromium.org/blink/trunk@166425 bbb929c8-8fbe-4397-9dbb-9b2b20218538