Cleanup: Remove getSmartClipData function from WebView API.

This function is only implemented by blink_web, but not called by
anyone, anywhere.

There are not callers of it on Blink nor on Chromium.

This fixes the TODO in WebView.h

BUG=None
TEST=None
R=abarth@chromium.org

Review URL: https://codereview.chromium.org/469693003

git-svn-id: svn://svn.chromium.org/blink/trunk@180138 bbb929c8-8fbe-4397-9dbb-9b2b20218538