Remove unnecessary casts and general code clean-up

pkg/analyzer/lib/src/dart/resolver/scope.dart

Index: pkg/analyzer/lib/src/dart/resolver/scope.dart
diff --git a/pkg/analyzer/lib/src/dart/resolver/scope.dart b/pkg/analyzer/lib/src/dart/resolver/scope.dart
index a3f0b07cda56dfddb14f93ad16a1d02ca2215709..54086d9dc144daadd579c61b2a1cbb33a6fdeba2 100644
--- a/pkg/analyzer/lib/src/dart/resolver/scope.dart
+++ b/pkg/analyzer/lib/src/dart/resolver/scope.dart
@@ -390,9 +390,9 @@ class LibraryImportScope extends Scope {
         }
       }
     }
-    if (foundElement is MultiplyDefinedElementImpl) {
-      foundElement = _removeSdkElements(
-          identifier, name, foundElement as MultiplyDefinedElementImpl);
+    Element element = foundElement;
+    if (element is MultiplyDefinedElementImpl) {
+      foundElement = _removeSdkElements(identifier, name, element);
     }
     if (foundElement is MultiplyDefinedElementImpl) {
       String foundEltName = foundElement.displayName;