get rid of s_files and files_lock

The only thing we need it for is alt-sysrq-r (emergency remount r/o)
and these days we can do just as well without going through the
list of files.

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

diff --cc fs/file_table.c
Simple merge

diff --cc fs/internal.h
Simple merge

diff --cc fs/open.c
Simple merge

diff --cc fs/super.c
Simple merge

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