Remove copy of WebFrameImpl* named TextFinder.

This was added in:
https://codereview.chromium.org/68263009/
but then the rest of the CLs never landed.

I've asked the author to start again.
TBR=tkent

Review URL: https://codereview.chromium.org/112083002

git-svn-id: svn://svn.chromium.org/blink/trunk@163569 bbb929c8-8fbe-4397-9dbb-9b2b20218538