analyzer: remove unused MultiplyInheritedExecutableElement

This is done as part of the 7.0.0 breaking change release.

Change-Id: I80c21e155f24dcf4c16f2c910e18b41a73633ca5
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/391560
Reviewed-by: Konstantin Shcheglov <[email protected]>
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Samuel Rawlins <[email protected]>

Author: srawlins

pkg/analyzer/CHANGELOG.md

@@ -32,6 +32,7 @@
 * Remove deprecated `source_io.dart`.
 * Remove deprecated `lint/Spelunker`.
 * Remove deprecated `source_resource.dart`.
+* Remove `MultiplyInheritedExecutableElement`.
 
 ## 6.11.0
 * Un-deprecated `LibraryElement.exportedLibraries`.

pkg/analyzer/lib/dart/element/element.dart

@@ -2119,15 +2119,6 @@ abstract class MultiplyDefinedElement implements Element {
   List<Element> get conflictingElements;
 }
 
-/// 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 MultiplyInheritedExecutableElement implements ExecutableElement {
-  /// The executable elements defined within this executable element.
-  List<ExecutableElement> get inheritedElements;
-}
-
 /// An object that controls how namespaces are combined.
 ///
 /// Clients may not extend, implement or mix-in this class.