Template directory is set in skin.json

Thanks to the upstream changes in T262067 we can make this template
directory relative to the skin and declare it inside skin.json

Bug: T262067
Change-Id: Ieccdf87979d14eeec0834b6b0cecf064d5fd9cfc

includes/SkinVector.php

@@ -89,7 +89,6 @@ class SkinVector extends SkinMustache {
 			unset( $options['link'] );
 		}
 
-		$options['templateDirectory'] = __DIR__ . '/templates';
 		parent::__construct( $options );
 	}
 

skin.json

@@ -24,6 +24,7 @@
 					"scripts": [
 						"skins.vector.js"
 					],
+					"templateDirectory": "includes/templates",
 					"responsive": true,
 					"styles": [
 						"mediawiki.ui.button",