Extract setCacheControlHeader from controller's context

lib/cartodb/controllers/named_maps.js

@@ -58,7 +58,7 @@ NamedMapsController.prototype.register = function(app) {
         setSurrogateKeyHeader({ surrogateKeysCache: this.surrogateKeysCache }),
         setCacheChannelHeader(),
         setLastModifiedHeader(),
-        this.setCacheControlHeader(),
+        setCacheControlHeader(),
         this.setContentTypeHeader(),
         this.respond(),
         vectorError()
@@ -87,7 +87,7 @@ NamedMapsController.prototype.register = function(app) {
         setSurrogateKeyHeader({ surrogateKeysCache: this.surrogateKeysCache }),
         setCacheChannelHeader(),
         setLastModifiedHeader(),
-        this.setCacheControlHeader(),
+        setCacheControlHeader(),
         this.setContentTypeHeader(),
         this.respond()
     );
@@ -465,7 +465,7 @@ function setLastModifiedHeader () {
     };
  }
 
-NamedMapsController.prototype.setCacheControlHeader = function () {
+function setCacheControlHeader () {
     return function setCacheControlHeaderMiddleware(req, res, next) {
         const { affectedTablesAndLastUpdate } = res.locals;
 
@@ -478,7 +478,7 @@ NamedMapsController.prototype.setCacheControlHeader = function () {
 
         next();
     };
- };
+ }
 
 NamedMapsController.prototype.setContentTypeHeader = function () {
     return function setContentTypeHeaderMiddleware(req, res, next) {