Revert r163981 "Show speech button for x-webkit-speech only if the field is editable and focused/hovered."

We're deprecating x-webkit-speech. So UI improvement is unnecessary. Also,
r163981 made a regression with two sites.

BUG=325496,332054,341015
TBR=keishi@chromium.org

Review URL: https://codereview.chromium.org/166183002

git-svn-id: svn://svn.chromium.org/blink/trunk@167160 bbb929c8-8fbe-4397-9dbb-9b2b20218538