udf: kill useless file header comments for vfs method implementations

There's not need to document vfs method invocation rules, we have
Documentation/filesystems/vfs.txt and Documentation/filesystems/Locking
for that.  Also a lot of these comments where either plain wrong or
horrible out of date.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>