Revert "ecrpytfs: Convert aio_read/write ops to read/write_iter"

This reverts commit 1e99f4d8eafbd5e8f6cd87b7465d499a6383a70b.
Revert "ext4: add support for read_iter and write_iter"

This reverts commit 8cdbcdf594dcae1b68463864ac10455cc990b38d.
Revert "fs: add read_iter and write_iter to several file systems"

This reverts commit b3e1d967fd302210cbf4051076d852d12acaa2a1.
Revert "fs: use read_iter and write_iter rather than aio_read and aio_write"

This reverts commit a6a7cefb3f2836dee65eadc760e132acf4ae848c.