Editable dropdown component improvement (#13389)

* replace Tree with List

* comments

src/sql/workbench/browser/modelComponents/dropdown.component.ts

@@ -70,8 +70,7 @@ export default class DropDownComponent extends ComponentBase<azdata.DropDownProp
 				strictSelection: false,
 				placeholder: '',
 				maxHeight: 125,
-				ariaLabel: '',
-				actionLabel: ''
+				ariaLabel: ''
 			};
 			this._editableDropdown = new Dropdown(this._editableDropDownContainer.nativeElement, this.contextViewService,
 				dropdownOptions);