Remove out of date comments from FontFallbackWin.h

Remove old out of date comments that no longer applies from
FontFallbackWin.h

TBR=dglazkov@chromium.org
BUG=

Review URL: https://codereview.chromium.org/176813011

git-svn-id: svn://svn.chromium.org/blink/trunk@167816 bbb929c8-8fbe-4397-9dbb-9b2b20218538