The {pinned} argument is always an empty register list now. Hence this
CL removes it.

R=jkummerow@chromium.org

Bug: v8:9919
Change-Id: I3b7612d90b0577f2763c5ab70c34eeb11307657b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1899607
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64761}