[mips][wasm-simd] Remove i8x16.mul

Port: 47ffa7a5

Bug: v8:6020
Change-Id: I4ae6261828b27f88553781a93d8557b6b685c217
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2719811


Auto-Submit: Liu yu <liuyu@loongson.cn>
Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#73069}