port 80dc6a33 https://crrev.com/c/1903445

Original Commit Message:

  [ptr-compr] Remove CompressedSigned MachineRepresentation

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

Change-Id: I3d656752bb81a09bd3985bd39ab9f656504f4da1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1911268
Auto-Submit: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Commit-Queue: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64925}