Revert 157488 "Re-enable an ASSERT in RenderTableSection::paint."

Causing use-after-frees on CF.

> Re-enable an ASSERT in RenderTableSection::paint.
> 
> The ASSERT triggered on table-section-node-at-point-crash.html,
> which why it was reverted. Testing locally, it doesn't seem to
> trigger anymore so let's re-enable it.
> 
> See http://trac.webkit.org/changeset/124641 for the story.
> 
> Review URL: https://chromiumcodereview.appspot.com/23604047

TBR=jchaffraix@chromium.org

Review URL: https://codereview.chromium.org/23708041

git-svn-id: svn://svn.chromium.org/blink/trunk@157798 bbb929c8-8fbe-4397-9dbb-9b2b20218538