fix(grid): remove aria-activedescendant on role="rowgroup"

Author: Volen99

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

@@ -1,5 +1,5 @@
 <div role="rowgroup" class="igx-grid-thead__wrapper" [style.width.px]="width"
-    [attr.aria-activedescendant]="activeDescendant" [class.igx-grid__tr--mrl]="hasMRL">
+    [class.igx-grid__tr--mrl]="hasMRL">
 
     <!-- Column headers area -->
     <div class="igx-grid__tr" role="row" [style.width.px]="width">