Fixed RBAC migration tests considering new signal handlers that are a bit too helpful during testing

We have some signal handlers now that perform work that do work
automatically that we want to explicitly test in our migration path, so
we have to undo some things in order to test the migration code.

awx/main/tests/functional/test_rbac_project.py

@@ -1,7 +1,7 @@
 import pytest
 
 from awx.main.migrations import _rbac as rbac
-from awx.main.models import Permission
+from awx.main.models import Permission, Role
 from django.apps import apps
 from awx.main.migrations import _old_access as old_access
 
@@ -24,6 +24,8 @@ def test_project_user_project(user_project, project, user):
 @pytest.mark.django_db
 def test_project_accessible_by_sa(user, project):
     u = user('systemadmin', is_superuser=True)
+    # This gets setup by a signal, but we want to test the migration which will set this up too, so remove it
+    Role.singleton('System Administrator').members.remove(u)
 
     assert project.accessible_by(u, {'read': True}) is False
     rbac.migrate_organization(apps, None)