Fixed remove mapping function

public/app/plugins/panel/singlestat/mappings.html

@@ -52,7 +52,7 @@
                         <div class="tight-form" ng-repeat="rangeMap in ctrl.panel.rangeMaps">
                                 <ul class="tight-form-list">
                                         <li class="tight-form-item">
-                                                <i class="fa fa-remove pointer" ng-click="ctrl.panel.removeRangeMap(rangeMap)"></i>
+                                                <i class="fa fa-remove pointer" ng-click="ctrl.removeRangeMap(rangeMap)"></i>
                                         </li>
                                         <li class="tight-form-item">
                                                 From