remove siphash subtree for forked version
Squashed 'siphash/' content from commit 89e7525

git-subtree-dir: siphash
git-subtree-split: 89e7525d01cccc653619962d5f9644b7f5b63c46
Merge commit '491d6c97cfcad89c4f459fd9cb576b01a7eb0319' as 'siphash'