Neither the TF backend nor Liftoff use the signature, thus remove it.

R=titzer@chromium.org

Bug: v8:8423
Change-Id: I909e9a0095cac67aaefaebcb4240f7d9829e4c87
Reviewed-on: https://chromium-review.googlesource.com/c/1373777Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#58190}