Revert "Consistently autosize vBulletin forum comments."

This patch reverts r157789 which autosized forum posts based on an
explicit check for vBulletin. In place of this check we are working on
three parallel efforts to fix this problem:
1) A more general solution to autosizing forum posts
2) A new autosizing implementation
3) Developer outreach.

For more information, see the following blink-dev discussion:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/gX9DE3SAohI

BUG=

Review URL: https://codereview.chromium.org/59653003

git-svn-id: svn://svn.chromium.org/blink/trunk@161682 bbb929c8-8fbe-4397-9dbb-9b2b20218538