Cleanup: remove unused import (#6345)

Remove unused import.

Author: japie1235813

tensorboard/webapp/metrics/views/right_pane/scalar_column_editor/scalar_column_editor_component.ts

@@ -20,9 +20,8 @@ import {
   Input,
   OnDestroy,
   Output,
-  ViewChild,
 } from '@angular/core';
-import {MatTabChangeEvent, MatTabGroup} from '@angular/material/tabs';
+import {MatTabChangeEvent} from '@angular/material/tabs';
 import {
   ColumnHeader,
   ColumnHeaderType,