[Telemetry] Don't format non-numeric values

Don't try to format non-numeric values; rather, just echo them back
directly. This is to allow simple printing of strings when received
on a telemetry subscription. Performed in the context of WTD-644
(since the WARP Server returns many such strings.)

platform/telemetry/src/TelemetryFormatter.js

@@ -22,7 +22,7 @@ define(
             }
 
             function formatRangeValue(v, key) {
-                return isNaN(v) ? "" : v.toFixed(3);
+                return isNaN(v) ? v : v.toFixed(3);
             }
 
             return {