Remove unused advances vector in FontHarfBuzz

Remove an unused Vector in FontHarfBuzz::drawGlyphs.

BUG=315149
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/60963002

git-svn-id: svn://svn.chromium.org/blink/trunk@161382 bbb929c8-8fbe-4397-9dbb-9b2b20218538