[mips] Fix kWasmInstanceOffset and clear an unused test

Fix a offset error, this is related to
commit 38fb1487

Delete cctest/test-run-machops/StackSlotAlignment, this is
related to commit a58f812c

Change-Id: I3ef1b96d8a3bdba530200cbac4f7a062496ace59
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2994813


Reviewed-by: Bill Budge <bbudge@chromium.org>
Reviewed-by: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Commit-Queue: Zhao Jiazhong <zhaojiazhong-hf@loongson.cn>
Auto-Submit: Liu yu <liuyu@loongson.cn>
Cr-Commit-Position: refs/heads/master@{#75493}