[wasm-simd] Remove scalar lowering tests

We already skip all tests on no-simd-sse builds, in effect not testing
scalar lowering. So, remove explicit tests for scalar lowering for all
other build configurations.

Cq-Include-Trybots: luci.v8.try:v8_linux_optional_rel_ng
Change-Id: I0aedad255236fa029e911bb9dc2dccab419791a4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2728249Reviewed-by: Deepti Gandluri <gdeepti@chromium.org>
Commit-Queue: Zhi An Ng <zhin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#73682}