example(architecture/dart): drop currency pipe workaround

Fixes angular#1898

Author: chalin

public/docs/_examples/architecture/dart/lib/sales_tax_component.dart

@@ -11,10 +11,7 @@ import 'tax_rate_service.dart';
 
       <div *ngIf="amountBox.value != ''">
       The sales tax is
-       {{ getTax(amountBox.value) | currency:'USD':false:'1.2-2' }}
-      <!-- would like to write currency:'USD':true:'1.2-2' but
-        currency as symbol is not currently supported; see
-        https://github.com/dart-lang/intl/issues/59 -->
+       {{ getTax(amountBox.value) | currency:'USD':true:'1.2-2' }}
       </div>
     ''',
     providers: const [SalesTaxService, TaxRateService])

public/docs/_examples/architecture/e2e-spec.ts

@@ -71,9 +71,7 @@ function salesTaxTests() {
   it('shows sales tax', async function () {
     let page = getPageElts();
     page.salesTaxAmountInput.sendKeys('10', protractor.Key.ENTER);
-    // Note: due to Dart bug USD is shown instead of $
-    let re = /The sales tax is (\$|USD)1.00/;
-    expect(page.salesTaxDetail.getText()).toMatch(re);
+    expect(page.salesTaxDetail.getText()).toEqual('The sales tax is $1.00');
   });
 }