[js_ast] Enable more lints

Change-Id: Ic206a3f1236943aa83a643c2d657b90c42a7968f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/420465
Reviewed-by: Nate Biggs <natebiggs@google.com>
Commit-Queue: Stephen Adams <sra@google.com>

pkg/js_ast/analysis_options.yaml

@@ -23,3 +23,5 @@ linter:
     - directives_ordering
     - prefer_single_quotes
     - prefer_relative_imports
+    - unnecessary_ignore
+    - unnecessary_statements