Remove unnecessary slicing in sdpa_attention_forward (#41900)
Remove redundant slicing in sdpa_attention_forward
The slicing in sdpa_attention_forward was there only because some masks were not constructed correctly (I was told). When the dimension is dynamic, the slice op also prevents torch.export from correctly reasoning about its size.
Signed-off-by: Justin Chu <justinchuby@users.noreply.github.com>