[MOV] developer/api/odoo: rename odoo.rst into external_api.rst

The previous file name was not very relevant in regard to the content of
the page, and it conflicted with the `sys.path`.

closes odoo/documentation#2064

Signed-off-by: Antoine Vandevenne (anv) <anv@odoo.com>

content/developer/reference/backend/security.rst

@@ -203,7 +203,7 @@ Unsafe Public Methods
 ---------------------
 
 Any public method can be executed via a :ref:`RPC call
-<api/odoo/calling_methods>` with the chosen parameters. The methods
+<api/external_api/calling_methods>` with the chosen parameters. The methods
 starting with a ``_`` are not callable from an action button or external API.
 
 On public methods, the record on which a method is executed and the parameters