Remove FontPlatformData::m_widthVariant.

The width variant is actually just a font feature request.
Now that HarfBuzzShaper::setFontFeatures() takes care of setting these
font features based on the FontDescription, there is no longer a need
to plumb these values though FontPlatformData.

Review URL: https://codereview.chromium.org/715363005

git-svn-id: svn://svn.chromium.org/blink/trunk@185391 bbb929c8-8fbe-4397-9dbb-9b2b20218538