This changes the WebAssembly pipeline to no longer expect source
position tables for {WasmCode} to be allocated on the GC'ed heap.

R=clemensh@chromium.org
BUG=v8:7721

Change-Id: Ib2c6e3d0840e47b83809f60519c0d1b94af186af
Reviewed-on: https://chromium-review.googlesource.com/1109686
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53961}