pkg/csslib: Remove a number of unused members, prepare for release

lib/src/polyfill.dart

Index: lib/src/polyfill.dart
diff --git a/lib/src/polyfill.dart b/lib/src/polyfill.dart
index bdd833031c1557024104b407232cca9e064f9f14..9b682ce4cb127126f0589830647683cd481c3f65 100644
--- a/lib/src/polyfill.dart
+++ b/lib/src/polyfill.dart
@@ -52,7 +52,7 @@ class PolyFill {
 
     // Resolve all definitions to a non-VarUsage (terminal expression).
     mainStyleSheetVarDefs.forEach((key, value) {
-      for (Expression expr in (value.expression as Expressions).expressions) {
+      for (var _ in (value.expression as Expressions).expressions) {
         mainStyleSheetVarDefs[key] =
             _findTerminalVarDefinition(_allVarDefinitions, value);
       }