Remove SVGSVGElement.viewport attribute

SVGSVGElement.viewport removed from the spec.
https://github.com/w3c/svgwg/commit/99a342c09dc0f8f164667d45d1c8486f0f87af8f

Intent to Remove:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/bFqDvZK2LVY

BUG=395838

Review-Url: https://codereview.chromium.org/2323653002
Cr-Commit-Position: refs/heads/master@{#417910}
13 files changed