Delete the FontPlatformData(const FontDescription&) constructor as it is
not implemented and never used.

R=derat@chromium.org

Review URL: https://codereview.chromium.org/469873002

git-svn-id: svn://svn.chromium.org/blink/trunk@180210 bbb929c8-8fbe-4397-9dbb-9b2b20218538