Remove unused copy of js_protocol.pdl

TBR=jgruber@chromium.org

Bug: v8:9247
Change-Id: I8024f701eae2a8b0d60fe859503089dd76b4d5bf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1681123Reviewed-by: Yang Guo <yangguo@chromium.org>
Commit-Queue: Yang Guo <yangguo@chromium.org>
Cr-Commit-Position: refs/heads/master@{#62441}