docs: filesystems: Remove uneeded .rst extension on toctables

There's no need to use a .rst on Sphinx toc tables. As most of
the Documentation don't use, remove the remaing occurrences.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/filesystems/ext4/index.rst

@@ -8,7 +8,7 @@ ext4 Data Structures and Algorithms
    :maxdepth: 6
    :numbered:
 
-   about.rst
-   overview.rst
-   globals.rst
-   dynamic.rst
+   about
+   overview
+   globals
+   dynamic