This reverts commit d16eefe0.

It is not correct to check for node equality during the graph
construction phase, because we can have optimizations that will combine
same nodes. So it can happen that in wasm-compiler, the inputs to
shuffle are not the same, so we canonicalize using that knowledge that
it will not be the same, and allow indices > 15. But later we can have
optimizations that combine the 2 inputs (e.g. splat of the same
constants), and the instruction selector will see that the input nodes
are the same.

Bug: v8:11542,chromium:1199662
Change-Id: I21c175f4707708038710147f64d687d1b14c6ecc
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2829986
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Bill Budge <bbudge@chromium.org>
Cr-Commit-Position: refs/heads/master@{#74017}