and use a newly-introduced "enum class Operation" in all
other places that so far passed Token::Values around.
Also delete some related dead code along the way.

Bug: v8:6921
Change-Id: I062f396d304aa62298cfeff202e3132a4a5597c1
Reviewed-on: https://chromium-review.googlesource.com/736851
Commit-Queue: Jakob Kummerow <jkummerow@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48944}