Specify the responsive option rather than manually specifying viewport

I6e69b482cdbc adds a viewport with the same value as Timeless.

Also remove the SkinTimeless::$skinname override, as it is now set in
Skin::__construct.

Bug: T258290
Depends-On: I6e69b482cdbc49c09adc6f7cee54f5e17b7c92c4
Change-Id: I215ac0153e5652e7ac76b11dba23a05aa2d1f685

includes/SkinTimeless.php

@@ -5,9 +5,6 @@
  * @ingroup Skins
  */
 class SkinTimeless extends SkinTemplate {
-	/** @var string */
-	public $skinname = 'timeless';
-
 	/** @var string */
 	public $stylename = 'Timeless';
 
@@ -20,11 +17,6 @@ class SkinTimeless extends SkinTemplate {
 	public function initPage( OutputPage $out ) {
 		parent::initPage( $out );
 
-		$out->addMeta( 'viewport',
-			'width=device-width, initial-scale=1.0, ' .
-			'user-scalable=yes, minimum-scale=0.25, maximum-scale=5.0'
-		);
-
 		$out->addModuleStyles( [
 			'mediawiki.skinning.content.externallinks',
 			'skins.timeless',

skin.json

@@ -11,7 +11,16 @@
 		"MediaWiki": ">= 1.34.0"
 	},
 	"ValidSkinNames": {
-		"timeless": "Timeless"
+		"timeless": {
+			"displayname": "Timeless",
+			"class": "SkinTimeless",
+			"args": [
+				{
+					"name": "timeless",
+					"responsive": true
+				}
+			]
+		}
 	},
 	"MessagesDirs": {
 		"Timeless": [