Remove QualifiedName argument from SVGElement::create functions

This is the SVG counterpart to r161742. As SVG is much more uniform, this
patch was simpler to put together, and it also makes use of the XML prefix
fixup code added in the earlier patch.

R=eseidel@chromium.org
BUG=316964

Review URL: https://codereview.chromium.org/68643007

git-svn-id: svn://svn.chromium.org/blink/trunk@161862 bbb929c8-8fbe-4397-9dbb-9b2b20218538