[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As these buttons points to demo.odoo.com, it is outdated very quickly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/bank/setup/create_bank_account.rst

@@ -42,12 +42,6 @@ support with this bank account.
     the company on your user preferences in order to add, edit or delete bank 
     accounts from another company.
 
-.. demo:fields:: base.action_res_partner_bank_account_form
-
-.. demo:action:: base.action_res_partner_bank_account_form
-
-   View *Bank Account* in our Online Demonstration
-
 .. todo:: add inherited field tooltip
 
     **Display on reports :** Display this bank account on the documents that

accounting/bank/setup/manage_cash_register.rst

@@ -17,10 +17,6 @@ Configuration
 2. In the tab Journal Entries, the Default Debit and Credit Account can be
    configured as well as the currency of the journal
 
-
-.. demo:fields:: account.action_account_journal_form
-
-
 Usage
 =====