It is unsound to look at the types in the TurboFan graphs after the
representation selection (and early optimization) phases, because

 (a) the remaining phases (might) run concurrently, and
 (b) the types may not be accurate (or even correct) after
     representation selection due to the way we deal with
     truncations.

So in Debug builds we now explicitly remove all types from the nodes
right after we uninstall the Typer decorator from the Graph, so any
further attempt to access the Type of a Node will lead to a crash (again
in Debug only for now).

CQ_INCLUDE_TRYBOTS=tryserver.v8:v8_linux64_tsan_rel
BUG=v8:4969
LOG=n

Review-Url: https://codereview.chromium.org/1937803002
Cr-Commit-Position: refs/heads/master@{#35920}