[REM] *: remove all demo.action buttons from the user documentation

- cherry-pick of e10581ef6e (see PR #572 )
- more fields deleted so that there was none left in 12.0

--> this makes the build of 12.0 much faster

*: accounting, inventory, purchase

As these buttons points to demo.odoo.com, it is outdated very quickly
and leads to weird results were a button on the 10.0 documentation
points to demo.odoo.com that runs 13.0 or no longer exists.

accounting/others/adviser/assets.rst

@@ -79,14 +79,6 @@ before confirming the asset.
    depreciation journal entries, not those related to the supplier
    bill.
 
-Explanation of the fields:
-
-.. demo:fields:: account_asset.action_account_asset_asset_form
-
-.. demo:action:: account_asset.action_account_asset_asset_form
-
-   Try creating an *Asset* in our online demonstration
-
 Create assets automatically from a supplier bill
 ================================================
 

accounting/others/configuration/account_type.rst

@@ -77,10 +77,4 @@ menu :menuselection:`Adviser --> Chart of Accounts`, the click on the
 **Create** button.
 
 .. image:: ./media/type01.png
-   :align: center
-
-.. demo:fields:: account.action_account_form
-
-.. demo:action:: account.action_account_form
-
-   View *Create Account* in our Online Demonstration
+   :align: center