Remove MultiplyInheritedExecutableElement2

Also removes the only reference to the old model equivalent.

Change-Id: I9dd30f4d7864eca6190df7ae5ebb419ea61e1f9d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/382683
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
diff --git a/pkg/analysis_server/lib/src/services/kythe/kythe_visitors.dart b/pkg/analysis_server/lib/src/services/kythe/kythe_visitors.dart
index 3c75ad8..542fbfd 100644
--- a/pkg/analysis_server/lib/src/services/kythe/kythe_visitors.dart
+++ b/pkg/analysis_server/lib/src/services/kythe/kythe_visitors.dart
@@ -150,7 +150,6 @@
 
   @override
   StringBuffer visitElement(Element element) {
-    assert(element is! MultiplyInheritedExecutableElement);
     var enclosingElt = element.enclosingElement!;
     var buffer = enclosingElt.accept(this)!;
     if (buffer.isNotEmpty) {
diff --git a/pkg/analyzer/lib/dart/element/element2.dart b/pkg/analyzer/lib/dart/element/element2.dart
index 5df54ac..27c875a 100644
--- a/pkg/analyzer/lib/dart/element/element2.dart
+++ b/pkg/analyzer/lib/dart/element/element2.dart
@@ -1336,16 +1336,6 @@
   List<Element2> get conflictingElements2;
 }
 
-/// An [ExecutableElement], with the additional information of a list of
-/// [ExecutableElement]s from which this element was composed.
-///
-/// Clients may not extend, implement or mix-in this class.
-abstract class MultiplyInheritedExecutableElement2
-    implements ExecutableElement2 {
-  /// The executable elements defined within this executable element.
-  List<ExecutableElement2> get inheritedElements2;
-}
-
 /// A pattern variable.
 ///
 /// Clients may not extend, implement or mix-in this class.