remove one more analyzer related TODO

lib/src/codegen/js_codegen.dart

Index: lib/src/codegen/js_codegen.dart
diff --git a/lib/src/codegen/js_codegen.dart b/lib/src/codegen/js_codegen.dart
index c0b39ff768bc3edc79ce4fc16151935b2c9ae907..dd157c8c59d808a3c68f297e1af7c0bffe7771cb 100644
--- a/lib/src/codegen/js_codegen.dart
+++ b/lib/src/codegen/js_codegen.dart
@@ -2495,8 +2495,6 @@ bool _isPotentiallyMutated(VariableElement e, [AstNode context]) {
 
 /// Adapted from VariableResolverVisitor. Finds an assignment to a given
 /// local variable.
-// TODO(jmesserly): change type annotation to not be *Impl once
-// isPotentiallyMutated is available on VariableElement.
 class _AssignmentFinder extends RecursiveAstVisitor {
   final VariableElement _variable;
   bool _potentiallyMutated = false;