docs: fix up the obviously obsolete bits in the new ext4 documentation

Signed-off-by: Theodore Ts'o <tytso@mit.edu>
diff --git a/Documentation/index.rst b/Documentation/index.rst
index 65c22b1..f95ba98 100644
--- a/Documentation/index.rst
+++ b/Documentation/index.rst
@@ -109,7 +109,7 @@
 subprojects.
 
 .. toctree::
-   :maxdepth: 4
+   :maxdepth: 2
 
    filesystems/ext4/index