fix(grid): header icon and text jump on focus

Author: simeonoff

projects/igniteui-angular/src/lib/core/styles/components/grid/_grid-theme.scss

@@ -1557,18 +1557,11 @@
     }
 
     %igx-grid__th--active {
-        @extend %grid-cell--active;
-
+        %grid-cell-header,
         %igx-grid__th--selected,
         %igx-grid__th--selectable {
             @extend %grid-cell--active
         }
-
-        %igx-grid__filtering-cell,
-        %grid-cell-header {
-            border-right: none;
-            border-bottom: none;
-        }
     }
 
     %igx-grid-summary--active {