[AOTI] Change the cpp wrapper codegen for sdpa (#120592)
Summary: Switch codegen for sdpa to always point to v2 in the C shim. Since aoti_torch__scaled_dot_product_flash_attention_v2 has been introduced for a while, there shouldn't be any FC issue in production.
Differential Revision: [D54258090](https://our.internmc.facebook.com/intern/diff/D54258090)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/120592
Approved by: https://github.com/chenyang78
ghstack dependencies: #119987
