Now the ModS opcode and MacroAssembler::EmitFPUTruncate function
are useless, and should be removed.

Change-Id: I5ba7c2cd01084b322046c8267b7581ab9d1755c6
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2554382Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#71352}