DevTools: Remove unused variables. Disallow unused variables with eslint

third_party/WebKit/Source/devtools/front_end/ui_lazy/DataGrid.js

Index: third_party/WebKit/Source/devtools/front_end/ui_lazy/DataGrid.js
diff --git a/third_party/WebKit/Source/devtools/front_end/ui_lazy/DataGrid.js b/third_party/WebKit/Source/devtools/front_end/ui_lazy/DataGrid.js
index 675221b5aae3a41004f02d9f479dcbcba3ca0d6d..a62d5df767af2c1fd05832322942ea59ae707f44 100644
--- a/third_party/WebKit/Source/devtools/front_end/ui_lazy/DataGrid.js
+++ b/third_party/WebKit/Source/devtools/front_end/ui_lazy/DataGrid.js
@@ -602,7 +602,6 @@ UI.DataGrid = class extends Common.Object {
       // when the two columns that get resized get a percent value for
       // their widths, all the other columns already have percent values
       // for their widths.
-      var headerTableColumns = this._headerTableColumnGroup.children;
 
       // Use container size to avoid changes of table width caused by change of column widths.
       var tableWidth = this.element.offsetWidth - this._cornerWidth;