branchcache: drop the unused `_verifyclosed` This code appears dead since its introduction about 5 years ago in this three consecutive commits: - 6578654916ae → introduce the method with two calls - 7c9d4cf23adf → remove first call - be5eeaf5c24a → remove second call o changeset: be5eeaf5c24a | user: Pulkit Goyal <pulkit@yandex-team.ru> | date: Fri Apr 05 15:57:09 2019 +0300 | summary: branchcache: don't verify closed nodes in _branchtip() | o changeset: 7c9d4cf23adf | user: Pulkit Goyal <pulkit@yandex-team.ru> | date: Fri Apr 05 15:56:33 2019 +0300 | summary: branchcache: don't verify closed nodes in iteropen() | o changeset: 6578654916ae | user: Pulkit Goyal <pulkit@yandex-team.ru> ~ date: Mon Apr 01 13:56:47 2019 +0300 summary: branchcache: lazily validate nodes from the branchmap