kill do_sync_read/do_sync_write

all remaining instances of aio_{read,write} (all 4 of them) have explicit
->read and ->write resp.; do_sync_read/do_sync_write is never called by
__vfs_read/__vfs_write anymore and no other users had been left.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

diff --cc fs/read_write.c
Simple merge

diff --cc include/linux/fs.h
Simple merge