[3.0 alpha] Remove deprecated dart:async APIs

Contributes to #49529

Change-Id: Ib70efd0f388f50686e1745ca5237d06a4538a870
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/268460
Reviewed-by: Sigmund Cherem <[email protected]>
Reviewed-by: Slava Egorov <[email protected]>

Author: mit-mit

CHANGELOG.md

@@ -9,6 +9,16 @@
   removed.  See [#49536](https://github.com/dart-lang/sdk/issues/49536) for
   details.
 
+#### `dart:async`
+
+- **Breaking change** [#49529][]:
+  - Removed the deprecated [`DeferredLibrary`][] class.
+    Use the [`deferred as`][] import syntax instead.
+
+[#49529]: https://github.com/dart-lang/sdk/issues/49529
+[`DeferredLibrary`]: https://api.dart.dev/stable/2.18.4/dart-async/DeferredLibrary-class.html
+[`deferred as`]: https://dart.dev/guides/language/language-tour#deferred-loading
+
 ## 2.19.0
 
 ### Language

sdk/lib/_internal/js_dev_runtime/patch/async_patch.dart

@@ -168,15 +168,6 @@ class _AsyncRun {
   }
 }
 
-@patch
-class DeferredLibrary {
-  @patch
-  Future<Null> load() {
-    throw 'DeferredLibrary not supported. '
-        'please use the `import "lib.dart" deferred as lib` syntax.';
-  }
-}
-
 @patch
 class Timer {
   @patch

sdk/lib/_internal/js_runtime/lib/async_patch.dart

@@ -91,15 +91,6 @@ class _AsyncRun {
   }
 }
 
-@patch
-class DeferredLibrary {
-  @patch
-  Future<Null> load() {
-    throw 'DeferredLibrary not supported. '
-        'please use the `import "lib.dart" deferred as lib` syntax.';
-  }
-}
-
 @patch
 class Timer {
   @patch

sdk/lib/_internal/vm/lib/async_patch.dart

@@ -10,7 +10,6 @@
 import "dart:_internal" show VMLibraryHooks, patch, unsafeCast;
 
 /// These are the additional parts of this patch library:
-part "deferred_load_patch.dart";
 part "schedule_microtask_patch.dart";
 part "timer_patch.dart";
 

sdk/lib/_internal/vm/lib/deferred_load_patch.dart

@@ -4,25 +4,6 @@
 
 part of dart.async;
 
-/// Indicates that loading of [libraryName] is deferred.
-///
-/// This class is obsolete. Instead prefer the `deferred as` import directive
-/// syntax.
-/// ```
-@Deprecated("Dart sdk v. 1.8")
-class DeferredLibrary {
-  final String libraryName;
-  final String? uri;
-
-  const DeferredLibrary(this.libraryName, {this.uri});
-
-  /// Ensure that [libraryName] has been loaded.
-  ///
-  /// If the library fails to load, the [Future] will complete with a
-  /// [DeferredLoadException].
-  external Future<Null> load();
-}
-
 /// Thrown when a deferred library fails to load.
 class DeferredLoadException implements Exception {
   DeferredLoadException(String message) : _s = message;