Revert the "helpful message" code

Remove the error message when there is no data or query. The problem
is, that is a valid usecase that we need to use.

src/singlevalue_ctrl.js

@@ -34,13 +34,13 @@ class SingleValueCtrl extends MetricsPanelCtrl {
         }
 
         const results = dataList[0];
-        const data = results && results.rows && results.rows[0];
-        if (!data) {
-            this.text = "No result rows. Make sure you are using 'Table' format and not 'Time series' format.";
-            this.url = null;
+
+        if (!results) {
             return;
         }
 
+        const data = results.rows && results.rows[0];
+
         // Substitute variables in the two templates
         const vars = {};
         for (let key in data) {