Migrate User.InferSystemInstallDate to sync by default (#11505)

* Migrate User.InferSystemInstallDate to sync by default

* Change var name

store/sqlstore/user_store.go

@@ -1488,15 +1488,13 @@ func (us SqlUserStore) ClearAllCustomRoleAssignments() *model.AppError {
 	return nil
 }
 
-func (us SqlUserStore) InferSystemInstallDate() store.StoreChannel {
-	return store.Do(func(result *store.StoreResult) {
-		createAt, err := us.GetReplica().SelectInt("SELECT CreateAt FROM Users WHERE CreateAt IS NOT NULL ORDER BY CreateAt ASC LIMIT 1")
-		if err != nil {
-			result.Err = model.NewAppError("SqlUserStore.GetSystemInstallDate", "store.sql_user.get_system_install_date.app_error", nil, err.Error(), http.StatusInternalServerError)
-			return
-		}
-		result.Data = createAt
-	})
+func (us SqlUserStore) InferSystemInstallDate() (int64, *model.AppError) {
+	createAt, err := us.GetReplica().SelectInt("SELECT CreateAt FROM Users WHERE CreateAt IS NOT NULL ORDER BY CreateAt ASC LIMIT 1")
+	if err != nil {
+		return 0, model.NewAppError("SqlUserStore.GetSystemInstallDate", "store.sql_user.get_system_install_date.app_error", nil, err.Error(), http.StatusInternalServerError)
+	}
+
+	return createAt, nil
 }
 
 func (us SqlUserStore) GetUsersBatchForIndexing(startTime, endTime int64, limit int) ([]*model.UserForIndexing, *model.AppError) {