Deployments: added missing 'delete deployment' endpoint

per https://docs.github.com/en/rest/reference/repos#delete-a-deployment

Author: clxmstaab

lib/Github/Api/Deployment.php

@@ -66,6 +66,23 @@ public function create($username, $repository, array $params)
         return $this->post('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/deployments', $params);
     }
 
+    /**
+     * Delete a deployment for the given username and repo.
+     *
+     * @link https://docs.github.com/en/rest/reference/repos#delete-a-deployment
+     *
+     * Important: Deployments can only be deleted when in inactive state
+     * @see updateStatus
+     *
+     * @param string $username   the user who owns the repo
+     * @param string $repository the name of the repo
+     * @param int    $id         the id of the deployment
+     */
+    public function remove($username, $repository, $id)
+    {
+        return $this->delete('/repos/'.rawurlencode($username).'/'.rawurlencode($repository).'/deployments/'.$id);
+    }
+    
     /**
      * Updates a deployment by creating a new status update.
      *