Revert "make flash_attn_bw impl correct w.r.t. meta when k and v have different strides (#119500)"
This reverts commit 095f4713077639f0e48fa33d051c0de2eb1f8525.
Reverted https://github.com/pytorch/pytorch/pull/119500 on behalf of https://github.com/DanilBaibak due to Broken trunk ([comment](https://github.com/pytorch/pytorch/pull/119500#issuecomment-1937003082))
