Revert "bio: add bvec_length(), like iov_length()"

This reverts commit ddd5f716dc8d13e92c4c9cd6ba13f946bde792f2.
Revert "aio: add aio support for iov_iter arguments"

This reverts commit 13b415423cd3beb397c2d980ee804f5e2def20f0.
Revert "aio: add aio_kernel_() interface"

This reverts commit ae07845967b4f01f7d11b2ae9f88a6fd57adccb6.