The tiers are now consistently referred to as baselin and top tier.

Bug: v8:9003
Change-Id: I74ad1867aca63bee9eb83b7f0f9fbaf2b1523dcb
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1547667
Commit-Queue: Frederik Gossen <frgossen@google.com>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60591}