Elements. Remove check for FragmentImpl in computeConstantValue(), it is always element.

Change-Id: I7cb9836458f988d39944ccafee97de90825bab9e
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/441361
Reviewed-by: Paul Berry <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/constant/evaluation.dart

@@ -80,11 +80,6 @@ class ConstantEvaluationEngine {
 
   /// Compute the constant value associated with the given [constant].
   void computeConstantValue(ConstantEvaluationTarget constant) {
-    if (constant is FragmentImpl) {
-      var element = constant as FragmentImpl;
-      constant = element.declaration as ConstantEvaluationTarget;
-    }
-
     var libraryFragment = constant.libraryFragment!;
     var library = libraryFragment.element;
     if (constant is FormalParameterElementImpl) {