title: Remove sorting menu from ui-grid column header
body: <p>I created ui-grid that has three columns, by default, the column header have a 'v' shaped icon (marked in red circle in the image) :</p>
  <p><a href="https://i.stack.imgur.com/IZDeh.png" rel="noreferrer"><img src="https://i.stack.imgur.com/IZDeh.png" alt="enter image description here" /></a></p>
  <p>Here the code and the plunker:</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>var app = angular.module('app', ['ngTouch', 'ui.grid', 'ui.grid.expandable', 'ui.grid.selection', 'ui.grid.pinning']);
  
  
  app.controller('ThirdCtrl', ['$scope', '$http', '$log', function ($scope, $http, $log) {
        $scope.gridOptions = {
          expandableRowTemplate: 'expandableRowTemplate.html',
          expandableRowHeight: 150,
          onRegisterApi: function (gridApi) {
              gridApi.expandable.on.rowExpandedStateChanged($scope, function (row) {
                  if (row.isExpanded) {
                    row.entity.subGridOptions = {
                      columnDefs: [
                      { name: 'name'},
                      { name: 'gender'},
                      { name: 'company'}
                    ]};
  
                    $http.get('https://cdn.rawgit.com/angular-ui/ui-grid.info/gh-pages/data/100.json')
                      .success(function(data) {
                        row.entity.subGridOptions.data = data;
                      });
                  }
              });
          }
        }
  
        $scope.gridOptions.columnDefs = [
          { name: 'id', pinnedLeft:true },
          { name: 'name'},
          { name: 'age'},
          { name: 'address.city'}
        ];
  
        $http.get('https://cdn.rawgit.com/angular-ui/ui-grid.info/gh-pages/data/500_complex.json')
          .success(function(data) {
            $scope.gridOptions.data = data;
          });
      }]);</code></pre>
  <pre class="snippet-code-css lang-css prettyprint-override"><code>.grid {
    width: 100%;
    height: 400px;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;!doctype html&gt;
  &lt;html ng-app="app"&gt;
    &lt;head&gt;
      &lt;script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.3/angular.js"&gt;&lt;/script&gt;
      &lt;script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.3/angular-touch.js"&gt;&lt;/script&gt;
      &lt;script src="http://ajax.googleapis.com/ajax/libs/angularjs/1.4.3/angular-animate.js"&gt;&lt;/script&gt;
      &lt;script src="http://ui-grid.info/docs/grunt-scripts/csv.js"&gt;&lt;/script&gt;
      &lt;script src="http://ui-grid.info/docs/grunt-scripts/pdfmake.js"&gt;&lt;/script&gt;
      &lt;script src="http://ui-grid.info/docs/grunt-scripts/vfs_fonts.js"&gt;&lt;/script&gt;
      &lt;script src="http://ui-grid.info/release/ui-grid.js"&gt;&lt;/script&gt;
      &lt;link rel="stylesheet" href="http://ui-grid.info/release/ui-grid.css" type="text/css"&gt;
      &lt;link rel="stylesheet" href="main.css" type="text/css"&gt;
    &lt;/head&gt;
    &lt;body&gt;
  
  
  &lt;div ng-controller="ThirdCtrl"&gt;
     &lt;div ui-grid="gridOptions" ui-grid-expandable class="grid"&gt;&lt;/div&gt;
  &lt;/div&gt;
  
  
      &lt;script src="app.js"&gt;&lt;/script&gt;
    &lt;/body&gt;
  &lt;/html&gt;</code></pre>
  </div>
  </div>
  </p>
  <p>In the image above the grid I have created in my project.</p>
  <p>My question is how can I remove the &quot;v&quot; sign in header row in red circle?</p>