Revert "Fix implementation of isDartCore and isDartAsync."

This reverts commit 0779751b82d5c98d335b531e68a0293b5caba90e.

Reason for revert: Broke test unittest-asserts-release-win:pkg/analyzer/test/generated/resolver_test (see https://ci.chromium.org/p/dart/builders/ci.sandbox/analyzer-win-release/5691)

Original change's description:
> Fix implementation of isDartCore and isDartAsync.
> 
> It's not sufficient to check the name of the library, since a
> user-provided library could always name itself `dart.core` or
> `dart.async`.
> 
> Change-Id: Id99cfc1ec89c5941e16b556e3c4dd175875a673f
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/104580
> Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
> Commit-Queue: Paul Berry <paulberry@google.com>

TBR=paulberry@google.com,brianwilkerson@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I7a27b46f4b2d1b3b43f9943933ec2a75b5a5b806
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/105346
Reviewed-by: Paul Berry <paulberry@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>
diff --git a/pkg/analyzer/lib/src/dart/element/element.dart b/pkg/analyzer/lib/src/dart/element/element.dart
index 0754e01..53cd4f7 100644
--- a/pkg/analyzer/lib/src/dart/element/element.dart
+++ b/pkg/analyzer/lib/src/dart/element/element.dart
@@ -6653,16 +6653,10 @@
       entryPoint != null && isOrImportsBrowserLibrary;
 
   @override
-  bool get isDartAsync {
-    var uri = definingCompilationUnit.source?.uri;
-    return uri != null && DartUriResolver.isDartUri(uri) && uri.path == 'async';
-  }
+  bool get isDartAsync => name == "dart.async";
 
   @override
-  bool get isDartCore {
-    var uri = definingCompilationUnit.source?.uri;
-    return uri != null && DartUriResolver.isDartUri(uri) && uri.path == 'core';
-  }
+  bool get isDartCore => name == "dart.core";
 
   @override
   bool get isInSdk {