[SVG] Remove calculateDeviceSpaceTransformation()

With most of the SVG record time rasterization out of the way, the only
client left for calculateDeviceSpaceTransformation() is
calculateScreenFontSizeScalingFactor(). Let's hide the ugly there.

R=fs@opera.com,schenney@chromium.org,pdr@chromium.org

Review URL: https://codereview.chromium.org/677443003

git-svn-id: svn://svn.chromium.org/blink/trunk@184305 bbb929c8-8fbe-4397-9dbb-9b2b20218538