move close_range(2) into fs/file.c, fold __close_range() into it

	We never had callers for __close_range() except for close_range(2)
itself.  Nothing of that sort has appeared in four years and if any users
do show up, we can always separate those suckers again.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>