On system which required a contiguous code range, we currently limit
the committed wasm code space to the heap code space. Since
https://crrev.com/c/1044195, this was only 128MB, making bigger
benchmarks fail.
There is no need to link the two limits, thus just remove that logic.

R=titzer@chromium.org

Change-Id: Id61f5dd28c96c3d2b7fcd730751285c6fc144bc5
Reviewed-on: https://chromium-review.googlesource.com/1049648Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53059}