Formats: Remove display & related method (#2776)

Format should not be responsible for sending HTTP response.

docs/08_Format_API/02_FormatInterface.md

@@ -14,14 +14,6 @@ Find a [template](#template) at the end of this file
 
 # Functions
 
-## The `display` function
-
-The `display` function shows the contents to the user and must return the object instance.
-
-```PHP
-display(): self
-```
-
 ## The `stringify` function
 
 The `stringify` function returns the items received by [`setItems`](#the-setitem-function) as string.
@@ -109,12 +101,6 @@ class MyTypeFormat implements FormatInterface {
         return ''; // Return items as string
     }
 
-    public function display(){
-        // Implement your code here
-        echo $this->stringify();
-        return $this;
-    }
-
     public function setItems(array $items){
         $this->items = $items;
         return $this;