netfs: fix documentation build error

Commit 86b374d0 ("netfs: Remove fs/netfs/io.c") did what it said on the
tin, but failed to remove the reference to fs/netfs/io.c from the
documentation, leading to this docs build error:

  WARNING: kernel-doc './scripts/kernel-doc -rst -enable-lineno -sphinx-version 7.3.7 ./fs/netfs/io.c' failed with return code 1

Remove the offending kernel-doc line, making the docs build process a
little happier.

Fixes: 86b374d0 ("netfs: Remove fs/netfs/io.c")
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/874j5nlu86.fsf@trenco.lwn.netSigned-off-by: Christian Brauner <brauner@kernel.org>

Documentation/filesystems/netfs_library.rst

@@ -592,4 +592,3 @@ API Function Reference
 
 .. kernel-doc:: include/linux/netfs.h
 .. kernel-doc:: fs/netfs/buffered_read.c
-.. kernel-doc:: fs/netfs/io.c