All filesystems have now been converted to use ->readahead, so
remove the ->readpages operation and fix all the comments that
used to refer to it.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: NChristoph Hellwig <hch@lst.de>
Reviewed-by: NAl Viro <viro@zeniv.linux.org.uk>
Acked-by: NAl Viro <viro@zeniv.linux.org.uk>