[IMP] mobile: remove explanations about Firebase

Firebase is now automatically configured

mobile/firebase.rst

@@ -4,76 +4,6 @@
 Mobile
 ======
 
-Setup your Firebase Cloud Messaging
-===================================
+As of Odoo 12.0, there is no configuration needed to enable push notifications
+in the mobile app.
 
-In order to have mobile notifications in our Android app, you need an
-API key.
-
-If it is not automatically configured (for instance for On-premise or
-Odoo.sh) please follow these steps below to get an API key for the
-android app.
-
-.. danger::
-   The iOS app doesn't support mobile notifications for Odoo
-   versions < 12.
-
-Firebase Settings
-=================
-
-Create a new project
---------------------
-
-First, make sure you to sign in to your Google Account. Then, go to
-`https://console.firebase.google.com <https://console.firebase.google.com/>`__
-and create a new project.
-
-.. image:: media/firebase01.png
-   :align: center
-
-Choose a project name, click on **Continue**, then click on **Create
-project**.
-
-When you project is ready, click on **Continue**.
-
-You will be redirected to the overview project page (see next
-screenshot).
-
-Add an app
-----------
-
-In the overview page, click on the Android icon.
-
-.. image:: media/firebase02.png
-   :align: center
-
-You must use "com.odoo.com" as Android package name. Otherwise, it will
-not work.
-
-.. image:: media/firebase03.png
-   :align: center
-
-No need to download the config file, you can click on **Next** twice and
-skip the fourth step.
-
-Get generated API key
----------------------
-
-On the overview page, go to Project settings:
-
-.. image:: media/firebase04.png
-   :align: center
-
-In **Cloud Messaging**, you will see the **API key** and the **Sender ID**
-that you need to set in Odoo General Settings.
-
-.. image:: media/firebase05.png
-   :align: center
-
-Settings in Odoo
-================
-
-Simply paste the API key and the Sender ID from Cloud Messaging.
-
-.. image:: media/firebase06.png
-   :align: center