doc: west: drop "Moving to West" doc page

Converting a "pre-west" Zephyr setup is not something we officially
support anymore so drop associated documentation.

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

Author: kartben

doc/develop/west/index.rst

@@ -43,7 +43,6 @@ each command.
    sign.rst
    zephyr-cmds.rst
    why.rst
-   moving-to-west.rst
    without-west.rst
 
 For details on west's Python APIs, see :ref:`west-apis`.