remove the nobh helpers

[Christoph Hellwig]

Hi all,

this series (against the pagecache for-next branch) removes the nobh
helpers which are a variant of the "normal" buffer head helpers with
special tradeoffs for machines with a lot of highmem, and thus rather
obsolete.  They pass xfstests, or in case of jfs at least get as far
as the baseline.

This might not be as nice as an actual iomap conversion, but already
removes some hairy code in the way of removing ->writepage.

Diffstat:
 Documentation/filesystems/ext2.rst |    2 
 fs/buffer.c                        |  324 -------------------------------------
 fs/ext2/ext2.h                     |    1 
 fs/ext2/inode.c                    |   51 -----
 fs/ext2/namei.c                    |   10 -
 fs/ext2/super.c                    |    6 
 fs/jfs/inode.c                     |   18 +-
 fs/mpage.c                         |   47 -----
 include/linux/buffer_head.h        |    8 
 include/linux/mpage.h              |    2 
 10 files changed, 29 insertions(+), 440 deletions(-)