Remove unused runtime setting screenfontsubstitutionenabled

This setting existed in WebKit but Chromium never changed it from its default value. We're removing all such unchanging settings in Blink, along with their associated code.

R=abarth@chromium.org
BUG=226711

Review URL: https://codereview.chromium.org/14109006

git-svn-id: svn://svn.chromium.org/blink/trunk@148461 bbb929c8-8fbe-4397-9dbb-9b2b20218538
[content shell] update content_shell test expectations

Unreviewed gardening

Review URL: https://codereview.chromium.org/14296004

git-svn-id: svn://svn.chromium.org/blink/trunk@148462 bbb929c8-8fbe-4397-9dbb-9b2b20218538
Remove setResponseContentDispositionEncodingFallbackArray and related code

R=abarth@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/14186004

git-svn-id: svn://svn.chromium.org/blink/trunk@148463 bbb929c8-8fbe-4397-9dbb-9b2b20218538