remove unused disabled$ variable

src/app/submission/form/collection/submission-form-collection.component.html

@@ -10,7 +10,7 @@
             class="btn btn-outline-primary"
             (blur)="onClose()"
             (click)="onClose()"
-            [disabled]="(disabled$ | async) || (processingChange$ | async)"
+            [disabled]="(processingChange$ | async)"
             ngbDropdownToggle>
       <span *ngIf="(processingChange$ | async)"><i class='fas fa-circle-notch fa-spin'></i></span>
       <span *ngIf="!(processingChange$ | async)">{{ selectedCollectionName$ | async }}</span>

src/app/submission/form/collection/submission-form-collection.component.ts

@@ -63,12 +63,6 @@ export class SubmissionFormCollectionComponent implements OnChanges, OnInit {
    */
   @Output() collectionChange: EventEmitter<SubmissionObject> = new EventEmitter<SubmissionObject>();
 
-  /**
-   * A boolean representing if this dropdown button is disabled
-   * @type {BehaviorSubject<boolean>}
-   */
-  public disabled$ = new BehaviorSubject<boolean>(true);
-
   /**
    * A boolean representing if a collection change operation is processing
    * @type {BehaviorSubject<boolean>}