Revert "fs: add read_iter and write_iter to several file systems"

This reverts commit 5726aef0b1e4ad8c0300556c39183b4cc6eae323.
Revert "fs: use read_iter and write_iter rather than aio_read and aio_write"

This reverts commit 09c0091a591bdda09f478f0924edca3860e4ba8b.
Revert "fs: create file_readable() and file_writable() functions"

This reverts commit 9792d1cb100407e4d6b67001b00f195a4dd4f0ba.
Revert "loop: use aio to perform io on the underlying file"

This reverts commit f796425bf2132ba0bc7597b348b3792ba39a1630.
Revert "bio: add bvec_length(), like iov_length()"

This reverts commit 6d0ab5ae5dc19ce7d7bee9ec473e25770e5e729d.
Revert "aio: add aio_kernel_() interface"

This reverts commit bef6383d55a00c582bc766bed0f52b3e283c8130.

Conflicts:
	fs/aio.c
	include/linux/aio.h