There are no users of class types left inside TurboFan, so we can nuke
them and thereby simplify the type system quite a bit.

R=mvstanton@chromium.org
BUG=v8:5267,v8:5270

Review-Url: https://codereview.chromium.org/2309753002
Cr-Commit-Position: refs/heads/master@{#39152}