docs(material/chips): remove unused field visible (#22978)

(cherry picked from commit 5391cad)

Author: jeripeierSBB

src/components-examples/material/chips/chips-autocomplete/chips-autocomplete-example.ts

@@ -15,7 +15,6 @@ import {map, startWith} from 'rxjs/operators';
   styleUrls: ['chips-autocomplete-example.css'],
 })
 export class ChipsAutocompleteExample {
-  visible = true;
   selectable = true;
   removable = true;
   separatorKeysCodes: number[] = [ENTER, COMMA];

src/components-examples/material/chips/chips-input/chips-input-example.ts

@@ -15,7 +15,6 @@ export interface Fruit {
   styleUrls: ['chips-input-example.css'],
 })
 export class ChipsInputExample {
-  visible = true;
   selectable = true;
   removable = true;
   addOnBlur = true;