Extract setLastModifiedHeader from controller's context

lib/cartodb/controllers/named_maps.js

@@ -57,7 +57,7 @@ NamedMapsController.prototype.register = function(app) {
         getTile(tileOptions),
         setSurrogateKeyHeader({ surrogateKeysCache: this.surrogateKeysCache }),
         setCacheChannelHeader(),
-        this.setLastModifiedHeader(),
+        setLastModifiedHeader(),
         this.setCacheControlHeader(),
         this.setContentTypeHeader(),
         this.respond(),
@@ -86,7 +86,7 @@ NamedMapsController.prototype.register = function(app) {
         incrementMapViews({ metadataBackend: this.metadataBackend }),
         setSurrogateKeyHeader({ surrogateKeysCache: this.surrogateKeysCache }),
         setCacheChannelHeader(),
-        this.setLastModifiedHeader(),
+        setLastModifiedHeader(),
         this.setCacheControlHeader(),
         this.setContentTypeHeader(),
         this.respond()
@@ -446,7 +446,7 @@ function setCacheChannelHeader () {
     };
 }
 
-NamedMapsController.prototype.setLastModifiedHeader = function () {
+function setLastModifiedHeader () {
     return function setLastModifiedHeaderMiddleware(req, res, next) {
         const { affectedTablesAndLastUpdate } = res.locals;
 
@@ -463,7 +463,7 @@ NamedMapsController.prototype.setLastModifiedHeader = function () {
 
         next();
     };
- };
+ }
 
 NamedMapsController.prototype.setCacheControlHeader = function () {
     return function setCacheControlHeaderMiddleware(req, res, next) {