Remove BlockExpression from the Kernel language.

lib/type_propagation/builder.dart

Index: lib/type_propagation/builder.dart
diff --git a/lib/type_propagation/builder.dart b/lib/type_propagation/builder.dart
index 5c2b3f62a570721fee420ac1402a91b51bbc03ad..ca1913608c26183d31b98db2d37e168cbee5bc63 100644
--- a/lib/type_propagation/builder.dart
+++ b/lib/type_propagation/builder.dart
@@ -1498,11 +1498,6 @@ class ExpressionBuilder extends ExpressionVisitor<int> {
     return build(node.body);
   }
 
-  int visitBlockExpression(BlockExpression node) {
-    statementBuilder.build(node.body);
-    return build(node.value);
-  }
-
   int buildInnerFunction(FunctionNode node, {VariableDeclaration self}) {
     int variable = builder.newFunction(node);
     if (self != null) {