keep function id location in block scoped function transformer

lib/6to5/transformation/transformers/spec/block-scoped-functions.js

@@ -11,9 +11,6 @@ exports.BlockStatement = function (node, parent) {
     var func = node.body[i];
     if (!t.isFunctionDeclaration(i)) continue;
 
-    // this is to avoid triggering the TDZ detection
-    func.id.loc = null;
-
     var declar = t.variableDeclaration("let", [
       t.variableDeclarator(func.id, t.toExpression(func))
     ]);