dart2js: Remove rethrow from the CPS and Tree IRs.

pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart

Index: pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
diff --git a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
index f43f2873d8262bab9b15eae8406e41b3c20d1a58..979647ac22a0f79b822200bba8dac7af5b0dfd3e 100644
--- a/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
+++ b/pkg/compiler/lib/src/tree_ir/tree_ir_tracer.dart
@@ -82,10 +82,6 @@ class BlockCollector extends StatementVisitor {
     _addStatement(node);
   }
 
-  visitRethrow(Rethrow node) {
-    _addStatement(node);
-  }
-
   visitUnreachable(Unreachable node) {
     _addStatement(node);
   }
@@ -276,10 +272,6 @@ class TreeTracer extends TracerUtil with StatementVisitor {
     printStatement(null, "throw ${expr(node.value)}");
   }
 
-  visitRethrow(Rethrow node) {
-    printStatement(null, "rethrow");
-  }
-
   visitUnreachable(Unreachable node) {
     printStatement(null, "unreachable");
   }