[REM] doc: outdated intersphinx mappings

ea6e7379a3 removed the few intersphinx
refs to sqlalchemy & django, so these mappings have not been necessary
in a year. This is especially annoying as the currently configured
sqlalchemy mapping has been very flaky / regularly failing.

Remove the mappings entirely.

closes odoo/odoo#30397

doc/conf.py

@@ -180,8 +180,6 @@ todo_include_todos = False
 intersphinx_mapping = {
     'python': ('https://docs.python.org/3/', None),
     'werkzeug': ('http://werkzeug.pocoo.org/docs/', None),
-    'sqlalchemy': ('http://docs.sqlalchemy.org/en/rel_0_9/', None),
-    'django': ('https://django.readthedocs.org/en/latest/', None),
 }
 
 github_user = 'odoo'