Remove obsolete comment in fs.h

This question was determined to be a bug which was fixed in
commit 4a3b0a49.

Signed-off-by: Andreas Gruenbacher <agruen@suse.de>
Cc: Jan Blunck <jblunck@suse.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>