remove setDueDate function now upstream bug is fixed

src/Issue.php

@@ -30,15 +30,6 @@ class Issue extends GiteaRepoData{
     return $this->request($this->url.'/comments','GET');
   }
 
-  /*
-  * this field is handled seperatly to the others! :/
-  * https://github.com/go-gitea/gitea/issues/8179
-  */
-  public function setDueDate(\DateTime $date){
-    $args=['due_date'=>$date->format('c')];
-    return $this->request($this->url.'/deadline','POST',$args);
-  }
-
   public function hasLabel($label){
     $id=$label->id;
     foreach($this->labels as $label){