Now that all WebAssembly code (including its lazy compile stub) has been
moved off the garbage-collected heap, we can determine the taggedness of
parameters purely from the {Code::Kind} and no longer need a dedicated
flag for it.

R=clemensh@chromium.org
BUG=v8:6792

Change-Id: If40b6763d042c19b937391fac8301a03b8ccc891
Reviewed-on: https://chromium-review.googlesource.com/999416Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52433}