Main changes:

- Remove the kUninitialized and kInvalidated cell type aliases. They
  were confusing because their meaning depended on the current value in
  the cell. I think kUninitialized was obsolete anyways.
- Remove a DCHECK from the compiler. The property that was asserted,
  while true, is irrelevant.
- Remove the obsolete function GetConstantType. The only left use was
  in the object printer, but it's pointless there because we already
  print the value anyways.

Change-Id: Ic718c8ba39aeb5bf18f588535dfb755a023cb144
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2536647Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Georg Neis <neis@chromium.org>
Cr-Commit-Position: refs/heads/master@{#71198}