input: docs: properly format ToC headings

"class:: toc-title" was a workaround for older Sphinx versions that are
no longer supported.

The canonical way to add a heading to the ToC is to use :caption:.
Do that.

Cc: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: linux-input@vger.kernel.org
Signed-off-by: Vegard Nossum <vegard.nossum@oracle.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20231027081830.195056-8-vegard.nossum@oracle.com

docs: fix nested numbering in the TOC

With Sphinx 1.6 nested numbering is reported as warning::

./input/joydev/index.rst:13: WARNING: input/joydev/joystick-api is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-func-open is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-func-close is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-func-ioctl is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-func-poll is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-ioc-adap-g-caps is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-ioc-adap-g-log-addrs is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-ioc-adap-g-phys-addr is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-ioc-dqevent is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-ioc-g-mode is already assigned section numbers (nested numbered toctree?)
./media/uapi/cec/cec-funcs.rst:8: WARNING: media/uapi/cec/cec-ioc-receive is already assigned section numbers (nested numbered toctree?)

TOC numbering is already set in::

./input/devices/index.rst:9:
./media/uapi/cec/cec-api.rst:19:

I guess the nested numbering in:

./input/joydev/index.rst
./media/uapi/cec/cec-funcs.rst

is just a C&P typo, so lets remove it.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Input: docs - update joystick documentation a bit

Consolidate use instructions and userspace API notes into the same chapter;
remove completely obsolete references, move into a separate subdirectory.

Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>