resourceloader: Remove wgAvailableSkins from mw.config

Added in 2011 for use in QUnit tests (r80790, r80792).

That was a terrible idea in hindsight, which I removed again in
2015 with 6b758fc982, and 0f9e4ca0fb.

If a need for it were to arise in the future, we'd export it
within the file module that needs it, or via addJsConfigVars()
on only the pages that need it – not globally.

Bug: T217772
Change-Id: I3885cacaa9b33e6947dbaf26f9b6839e19588603

RELEASE-NOTES-1.33

@@ -279,6 +279,7 @@ because of Phabricator reports.
   * The transitional wrapper classes AuthPluginPrimaryAuthenticationProvider,
     AuthManagerAuthPlugin, and AuthManagerAuthPluginUser.
   * The $wgAuth configuration setting and its use in Setup.php and unit tests
+* (T217772) The 'wgAvailableSkins' mw.config key in JavaScript, was removed.
 
 === Deprecations in 1.33 ===
 * The configuration option $wgUseESI has been deprecated, and is expected

includes/resourceloader/ResourceLoaderStartUpModule.php

@@ -107,7 +107,6 @@ class ResourceLoaderStartUpModule extends ResourceLoaderModule {
 			'wgSiteName' => $conf->get( 'Sitename' ),
 			'wgDBname' => $conf->get( 'DBname' ),
 			'wgExtraSignatureNamespaces' => $conf->get( 'ExtraSignatureNamespaces' ),
-			'wgAvailableSkins' => Skin::getSkinNames(),
 			'wgExtensionAssetsPath' => $conf->get( 'ExtensionAssetsPath' ),
 			// MediaWiki sets cookies to have this prefix by default
 			'wgCookiePrefix' => $conf->get( 'CookiePrefix' ),