drop the _bullshit types and the transmutation

Placing a 16-byte aligned type at the start of the tuple struct seems to
fix the issues with BLAKE2b and BLAKE2p.
Remove BLAKE2bp and BLAKE2sp for now.

They're extremely broken because I cannot arrange for the correct
alignment of the blake2x_state structs in the arrays. This is pending
https://github.com/rust-lang/rust/issues/17537.