Avoid to silently ignore non-existing parameters

All the parameters $wgMatomo* should exist and have a default value.
Previously $wgMatomoIgnoreEditors was used but not defined. Now it will
return a ConfigException in such cases – which should not never occur.

src/Hooks.php

@@ -38,10 +38,8 @@ public static function getParameter( $name ) {
 		$config = \MediaWiki\MediaWikiServices::getInstance()->getMainConfig();
 		if ( $config->has( "Piwik$name" ) ) {
 			return $config->get( "Piwik$name" );
-		} elseif ( $config->has( "Matomo$name" ) ) {
-			return $config->get( "Matomo$name" );
 		}
-		return null;
+		return $config->get( "Matomo$name" );
 	}
 
 	/**