Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart

Index: pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart b/pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart
index bc4867dd3e83eb34393f19a117fc7b9d2b59e892..a4d445f76522d0474dfbf8b29aef79f810871a4e 100644
--- a/pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend_ast_nodes.dart
@@ -1047,7 +1047,6 @@ class Unparser {
 
   void writeParameters(Parameters params) {
     write('(');
-    bool first = true;
     writeEach(',', params.requiredParameters, (Parameter p) {
       if (p.type != null) {
         writeType(p.type);
@@ -1576,4 +1575,4 @@ class OpenStringChunk {
   StringChunk end(int endIndex) {
     return new StringChunk(previous, quoting, endIndex);
   }
-}
+}