simplify sdpa backward meta registration (#101128)
Per title.
there's an off chance that query_reshaped etc was actually discontiguous after reshape, but even in that case I'm pretty sure the computed gradients would still be contiguous, and we are properly transposing output gradients to produce correct strides.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/101128
Approved by: https://github.com/drisspg
