We no longer implement part of the debugger in JS. Therefore we can
remove the infrastructure to support this in the bootstrapper.

Also includes some drive-by cleanups.

Bug: v8:5530

R=petermarshall@chromium.org

Change-Id: I06628a559c17f99c70029fcc94848b0c78f1d3e9
Reviewed-on: https://chromium-review.googlesource.com/c/1369945
Commit-Queue: Yang Guo <yangguo@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58140}