This reverts commit 009993ad.

Reason for revert: New test fails, see https://ci.chromium.org/p/v8/builders/ci/V8%20Linux/35534 and https://ci.chromium.org/p/v8/builders/ci/V8%20Win32%20-%20debug/23778

Original change's description:
> [liftoff][wasm-simd] Implement f32x4.splat
> 
> Implement f32x4.splat and enable handling this in Liftoff.
> 
> We add a new macro for defining test cases to run on TurboFan, Liftoff,
> interpreter, and scalar lowering.
> 
> Also add an assertion that the execution tier used is what we expected
> it to be. This is useful for Liftoff, because by default it falls back
> to TurboFan when it encounters an unimplemented opcode.
> 
> Bug: v8:9909
> Change-Id: I594955fce778173191fc44c38c4f956a05e77839
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2014753
> Commit-Queue: Zhi An Ng <zhin@chromium.org>
> Reviewed-by: Clemens Backes <clemensb@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#65954}

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

Change-Id: Ie6970a8c29baab149150dd734a95f89be5fd89ff
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: v8:9909
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2017722Reviewed-by: Clemens Backes <clemensb@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65958}