Remove some unused functions in WebRuntimeFeatures

There is no callers for these functions in
Chromium so they can be safely removed.

Review URL: https://codereview.chromium.org/334473002

git-svn-id: svn://svn.chromium.org/blink/trunk@175975 bbb929c8-8fbe-4397-9dbb-9b2b20218538