doc: hardware: porting: remove old hwmv1 section

Drop the section describing hwmv1 board extensions since hwmv1 is no
longer supported.

Signed-off-by: Benjamin Cabé <[email protected]>

Author: kartben

doc/hardware/porting/board_porting.rst

@@ -974,50 +974,3 @@ extending a board.
    ├── Kconfig.plank
    ├── Kconfig.defconfig
    └── plank_<new-qualifiers>.yaml
-
-Board extensions (Old hardware model)
-*************************************
-
-.. note::
-
-  This extension mechanism is intended for boards in old hardware description
-  format. For boards described in new hardware model format, use the extension
-  feature described in :ref:`extend-board`.
-
-Boards already supported by Zephyr can be extended by downstream users, such as
-``example-application`` or vendor SDKs. In some situations, certain hardware
-description or :ref:`choices <devicetree-chosen-nodes>` can not be added in the
-upstream Zephyr repository, but they can be in a downstream project, where
-custom bindings or driver classes can also be created. This feature may also be
-useful in development phases, when the board skeleton lives upstream, but other
-features are developed in a downstream module.
-
-Board extensions are board fragments that can be present in an out-of-tree board
-root folder, under ``${BOARD_ROOT}/boards/extensions``. Here is an example
-structure of an extension for the ``plank`` board and its revisions:
-
-.. code-block:: none
-
-   boards/extensions/plank
-   ├── plank.conf                # optional
-   ├── plank_<revision>.conf     # optional
-   ├── plank.overlay             # optional
-   └── plank_<revision>.overlay  # optional
-
-A board extension directory must follow the naming structure of the original
-board it extends. It may contain Kconfig fragments and/or devicetree overlays.
-Extensions are, by default, automatically loaded and applied on top of board
-files, before anything else. There is no guarantee on which order extensions are
-applied, in case multiple exist. This feature can be disabled by passing
-``-DBOARD_EXTENSIONS=OFF`` when building.
-
-Note that board extensions need to follow the
-:ref:`same guidelines <porting-general-recommendations>` as regular boards. For
-example, it is wrong to enable extra peripherals or subsystems in a board
-extension.
-
-.. warning::
-
-   Board extensions are not allowed in any module referenced in Zephyr's
-   ``west.yml`` manifest file. Any board changes are required to be submitted to
-   the main Zephyr repository.