Remove phpstan ignoreErrors entries

Refers https://github.com/cakephp/cakephp/pull/13089#pullrequestreview-223025773

phpstan.neon

@@ -24,7 +24,6 @@ parameters:
         - '#Call to an undefined method Cake\\Auth\\Storage\\StorageInterface::setConfig\(\)#'
         - '#Variable \$_SESSION in isset\(\) always exists and is not nullable#'
         - '#PHPDoc tag @throws with type PHPUnit\\Exception is not subtype of Throwable#'
-        - '#Call to an undefined method PHPUnit\\Framework\\MockObject\\MockObject#'
         - '#Call to an undefined method DOMNode::setAttribute\(\)#'
         - '#Binary operation "\+" between array|false and array results in an error#'
         - '#Result of method Cake\\Auth\\BaseAuthenticate::unauthenticated\(\) \(void\) is used#'