Remove unused import which shares prefix name with a used import. (#59160)

Due to a bug in analyzer [1], some unused imports are not reported when
multiple import directives share a prefix name, and one or more are unused.

[1] https://github.com/dart-lang/sdk/issues/38784

packages/flutter_localizations/lib/src/cupertino_localizations.dart

@@ -7,7 +7,6 @@ import 'dart:async';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/foundation.dart';
 import 'package:intl/intl.dart' as intl;
-import 'package:intl/date_symbols.dart' as intl;
 
 import 'l10n/generated_cupertino_localizations.dart';
 import 'utils/date_localizations.dart' as util;

packages/flutter_localizations/lib/src/material_localizations.dart

@@ -7,7 +7,6 @@ import 'dart:async';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:intl/intl.dart' as intl;
-import 'package:intl/date_symbols.dart' as intl;
 
 import 'cupertino_localizations.dart';
 import 'l10n/generated_material_localizations.dart';