Revert r160156 "Enable SVG WebGL textures"

Introduces failing tests: http://test-results.appspot.com/dashboards/flakiness_dashboard.html#group=%40ToT%20Blink&tests=fast/canvas/webgl/tex-image-and-sub-image-2d-with-svg-image.html

TBR=pdr
BUG=

Review URL: https://codereview.chromium.org/34953003

git-svn-id: svn://svn.chromium.org/blink/trunk@160208 bbb929c8-8fbe-4397-9dbb-9b2b20218538