Turboprop has gotten faster lately, let's remove the SLOW flag.

Bug: v8:10894
Change-Id: I6fa5255264129d69295aff2a35b10c540f4b975f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2610970
Auto-Submit: Sathya Gunasekaran  <gsathya@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71949}