Control-flow aware allocation has been enabled by default for a long
time now. This removes the unused code paths related to splintering.

R=neis@chromium.org

Bug: v8:10933
Change-Id: I19d9eb448c3912b24a1ad16030e7dd556b13accc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2434328Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Thibaud Michaud <thibaudm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70172}