[DollbooruBridge] Remove bridge

The target site for this bridge has been down for at least a year
now and there doesn't seem to be any attempt to get it back up.
Their twitter account is also silent since 2012, so no harm
removing this bridge.

https://twitter.com/dollbooru?lang=en

bridges/DollbooruBridge.php

@@ -1,9 +0,0 @@
-<?php
-require_once('Shimmie2Bridge.php');
-
-class DollbooruBridge extends Shimmie2Bridge {
-	const MAINTAINER = 'mitsukarenai';
-	const NAME = 'Dollbooru';
-	const URI = 'http://dollbooru.org/';
-	const DESCRIPTION = 'Returns images from given page';
-}