docs: remove unused StringSafeDatePipe from AngularJS Quick Ref example (#28592)

PR Close #28592

aio/content/examples/ajs-quick-reference/src/app/date.pipe.ts

@@ -1,14 +0,0 @@
-import { Injectable, Pipe, PipeTransform } from '@angular/core';
-import { DatePipe } from '@angular/common';
-
-@Injectable()
-// #docregion date-pipe
-@Pipe({name: 'date', pure: true})
-export class StringSafeDatePipe extends DatePipe implements PipeTransform {
- transform(value: any, format: string): string {
-   value = typeof value === 'string' ?
-           Date.parse(value) : value;
-   return super.transform(value, format);
- }
-}
-// #enddocregion date-pipe