Remove BlockExpression from the Kernel language.

lib/visitor.dart

Index: lib/visitor.dart
diff --git a/lib/visitor.dart b/lib/visitor.dart
index 409c949a40b6253ee86651351d9410e5eb88801d..4b0fa070ffeaba2812b4a38a7cb1aa87bba70e87 100644
--- a/lib/visitor.dart
+++ b/lib/visitor.dart
@@ -51,7 +51,6 @@ abstract class ExpressionVisitor<R> {
   R visitBoolLiteral(BoolLiteral node) => defaultBasicLiteral(node);
   R visitNullLiteral(NullLiteral node) => defaultBasicLiteral(node);
   R visitLet(Let node) => defaultExpression(node);
-  R visitBlockExpression(BlockExpression node) => defaultExpression(node);
 }
 
 abstract class StatementVisitor<R> {
@@ -156,7 +155,6 @@ class TreeVisitor<R>
   R visitBoolLiteral(BoolLiteral node) => defaultBasicLiteral(node);
   R visitNullLiteral(NullLiteral node) => defaultBasicLiteral(node);
   R visitLet(Let node) => defaultExpression(node);
-  R visitBlockExpression(BlockExpression node) => defaultExpression(node);
 
   // Statements
   R defaultStatement(Statement node) => defaultTreeNode(node);