Since smi-corrputing, TaggedSigned (aka known smis) only have the lower
bits used. This renders CompressedSigned useless.

Bug: v8:7703
Change-Id: Id59aaebc24d670ed32c483ceecf77fd194405ee4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1903445
Commit-Queue: Santiago Aboy Solanes <solanes@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64883}