Revert "Flash Attention v2 (#105602)" (#108827)
This reverts commit add45aea1cc8048fd0b43445b28fec7d93281f00.
There are some conflicts on some benchmark csv file https://github.com/pytorch/pytorch/pull/105602#issuecomment-1710988951 so I need to revert this manually.
The diff has been reverted internally.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/108827
Approved by: https://github.com/kit1980
