Fix depreciation warnings in FileBackend construction

Added wikiId and lockManager was changed to an object
Bug: 58615

Change-Id: Id3bdc7e6bc3951db4753553da03193783f0bd7c8

MathTexvc.php

@@ -272,7 +272,8 @@ class MathTexvc extends MathRenderer {
 			if ( !$backend ) {
 				$backend = new FSFileBackend( array(
 					'name'           => 'math-backend',
-					'lockManager'    => 'nullLockManager',
+					'wikiId' 	 => wfWikiId(),
+					'lockManager'    => new NullLockManager(array() ),
 					'containerPaths' => array( 'math-render' => $wgMathDirectory ),
 					'fileMode'       => 0777
 				) );