Revert "fix up types.toStatement and return an expressionStatement if all else fails"

This reverts commit 740193b1e2.

lib/6to5/types/index.js

@@ -119,12 +119,18 @@ t.toStatement = function (node, ignore) {
   } else if (t.isFunction(node)) {
     mustHaveId = true;
     newType = "FunctionDeclaration";
-  } else {
-    return t.expressionStatement(node);
   }
 
   if (mustHaveId && !node.id) {
-    throw new Error("the type " + node.type + " needs an id in order to be transformed into a statement");
+    newType = false;
+  }
+
+  if (!newType) {
+    if (ignore) {
+      return false;
+    } else {
+      throw new Error("cannot turn " + node.type + " to a statement");
+    }
   }
 
   node.type = newType;