The JSToInteger operator is not used anywhere in TurboFan nowadays, so
no point in keeping the dead code in the tree.

Bug: v8:8015
Change-Id: If03ba63c4b932ba0aac60b9bbc89fee3909a93c6
Reviewed-on: https://chromium-review.googlesource.com/1238238Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56126}