Remove references to third_party/hyphen/hyph_en_US.dic .

I deleted support for -webkit-hyphen: last week, but missed
this reference.

BUG=268677
R=ojan@chromium.org

Review URL: https://codereview.chromium.org/22325004

git-svn-id: svn://svn.chromium.org/blink/trunk@155619 bbb929c8-8fbe-4397-9dbb-9b2b20218538