This reverts commit dfbbb4a5.

Reason for revert: Bitmask added post 84 cut, so it is not part of origin trial. Therefore it is still a post-mvp.

Original change's description:
> [wasm-simd] Add bitmask to SIMD MVP
> 
> This removes the post-mvp flag for bitmask, since it was accepted into
> the proposal, see https://github.com/WebAssembly/simd/pull/201.
> 
> Bug: v8:10308
> Change-Id: I4ced43a6484660125d773bc9de46bdea9f72b13b
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2216532
> Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
> Commit-Queue: Zhi An Ng <zhin@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#67993}

TBR=gdeepti@chromium.org,zhin@chromium.org

# Not skipping CQ checks because original CL landed > 1 day ago.

Bug: v8:10308
Change-Id: I53294be4ea816f37c7cc5f545afb572538dd4770
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2233183Reviewed-by: Zhi An Ng <zhin@chromium.org>
Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68216}