Remove --standalone argument from upgrade script

The --standalone option was removed at [1], the upgrade sript
still has the option that is why it was failing.

[1] - https://review.opendev.org/c/openstack/python-tripleoclient/+/753447
Closes-bug: #1943462

Change-Id: I4f88fa159928bdc0446c5bc85cc1c62e352ca9cc

roles/standalone-upgrade/templates/standalone.sh.j2

@@ -16,5 +16,7 @@ sudo openstack tripleo upgrade $PROMPT_ANSWER \
 {% if standalone_custom_env_files %}
   -e {{ standalone_custom_env_files | join(' -e ') }} \
 {% endif %}
-  --output-dir {{ working_dir }}/tripleo-deploy \
-  --standalone
+{% if release in ['stein', 'train', 'ussuri'] %}
+  --standalone \
+{% endif %}
+  --output-dir {{ working_dir }}/tripleo-deploy