Remove keyboard event filtering in fullscreen

Intent to Deprecate and Remove:
https://groups.google.com/a/chromium.org/d/msg/blink-dev/eeGNNCIBkX8/5KzPyK2caoUJ

BUG=428348

Review URL: https://codereview.chromium.org/681113006

git-svn-id: svn://svn.chromium.org/blink/trunk@185081 bbb929c8-8fbe-4397-9dbb-9b2b20218538