chore(*): Remove back track function due to duplicate keys.

Author: skrustev

projects/igniteui-angular/src/lib/grids/pivot-grid/pivot-header-row.component.html

@@ -278,7 +278,7 @@
                 }
             }
             <div class="igx-grid-thead--virtualizationWrapper" [style.max-height.px]="maxContainerHeight" (click)="grid.navigation.focusOutRowHeader($event)">
-                @for (dimLevelColumns of columnDimensionsByLevel; track trackColumnDimensionByLevel(dimLevelColumns); let i = $index) {
+                @for (dimLevelColumns of columnDimensionsByLevel; track $index; let i = $index) {
                     <div class="igx-grid-thead__group igx-grid-thead--virtualizationContainer" [style.height.px]="totalDepth > 1 ? grid.rowHeight : undefined" [style.width.px]="grid.unpinnedWidth">
                         <ng-template igxGridFor #headerVirtualContainer let-column
                             [igxGridForOf]="dimLevelColumns" [igxGridForOfUniqueSizeCache]="true" [igxForScrollContainer]="grid.parentVirtDir"

projects/igniteui-angular/src/lib/grids/pivot-grid/pivot-header-row.component.ts

@@ -203,15 +203,6 @@ export class IgxPivotHeaderRowComponent extends IgxGridHeaderRowComponent implem
         return this.totalDepth * this.grid.renderedRowHeight;
     }
 
-    /**
-    * @hidden
-    * @internal
-    * Use tracking function to fix ngFor not clearing old records from the DOM while updating it, causing incorrect header height during _calculateGridBodyHeight.
-    */
-    public trackColumnDimensionByLevel(item: IgxColumnComponent[]) {
-        return item.map(col => col.field).join('-');
-    }
-
     /**
     * @hidden
     * @internal