Remove unused parameters from LoadFontPromiseResolver

After r162940, LoadFontPromiseResolver::loaded() does not need Document.

TEST=none; no behavior changes.

Review URL: https://codereview.chromium.org/107373005

git-svn-id: svn://svn.chromium.org/blink/trunk@164525 bbb929c8-8fbe-4397-9dbb-9b2b20218538