Convert all but 4 Node*s to TNode and all Variables to TVariable.

In the process this also deletes several unused functions.

Bug: v8:6949, v8:9396
Change-Id: I83db40eefacf8a4a1b155249c5bb8217e6c7da83
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1803347
Commit-Queue: Dan Elphick <delphick@chromium.org>
Reviewed-by: Santiago Aboy Solanes <solanes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#63770}