remotefilelog: rework workaround for sshpeer deadlocks The wrapping of `sshpeer.cleanup` silently broke when `cleanup` was renamed to `_cleanup`, a couple of years ago. I don't know what `orig.im_self` is, but regardless, the intention of the wrapping seems pretty clear: close stderr before sshpeer._cleanuppipes blocks on it. So do that. Differential Revision: https://phab.mercurial-scm.org/D9997

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