clean up duplicated user creation code (#50178) (#50327)

* clean up duplicated user creation code

* remove unused duplicate getOrCreateOrg function

* fix up tests

(cherry picked from commit 9350ab781c)

pkg/tests/api/plugins/api_plugins_test.go

@@ -107,6 +107,9 @@ func TestPlugins(t *testing.T) {
 func createUser(t *testing.T, store *sqlstore.SQLStore, cmd models.CreateUserCommand) {
 	t.Helper()
 
+	store.Cfg.AutoAssignOrg = true
+	store.Cfg.AutoAssignOrgId = 1
+
 	_, err := store.CreateUser(context.Background(), cmd)
 	require.NoError(t, err)
 }