[REM] index: remove references to mementos

Because:
- Mementos are already referenced multiple times in related toctrees.
- Only two mementos are remaining, which is not enough to justify a whole doc category.
- References to mementos are easily broken without being detected at compilation time.

business.rst

@@ -1,9 +0,0 @@
-==================
-Business Mementos
-==================
-
-.. toctree::
-    Accounting Memento (US GAAP) <https://odoo.com/documentation/user/accounting/overview/main_concepts/memento.html>
-    Double-Entry Inventory <https://odoo.com/documentation/user/inventory/overview/concepts/double-entry.html>
-    Inventory Valuation (Continental Accounting) <https://odoo.com/documentation/user/inventory/management/reporting/inventory_valuation_config.html>
-    Inventory Valuation (Anglo-Saxon Accounting) <https://odoo.com/documentation/user/inventory/management/reporting/inventory_valuation_config.html>

conf.py

@@ -296,11 +296,7 @@ texinfo_documents = [
 # If true, do not generate a @detailmenu in the "Top" node's menu.
 #texinfo_no_detailmenu = False
 
-odoo_cover_external = {
-    'https://odoo.com/documentation/user/accounting/overview/main_concepts/memento.html'   : 'banners/m_accounting.jpg',
-    'https://odoo.com/documentation/user/inventory/overview/concepts/double-entry.html' : 'banners/m_1.jpg',
-    'https://odoo.com/documentation/user/inventory/management/reporting/inventory_valuation_config.html'    : 'banners/m_2.jpg',
-}
+odoo_cover_external = {}
 
 github_user = 'odoo'
 github_project = 'documentation-user'

index.rst

@@ -10,4 +10,3 @@ Odoo User Documentation
     Index <self>
     applications
     practical
-    business