sshpeer: remove frivolous call to _cleanup() _validaterepo() is called once during __init__. _cleanup() no-ops if the self._pipe* attributes aren't set. These attributes are set during _validaterepo(). So the call to _cleanup() isn't necessary. But just to be on the safe side, we add an assertion. Differential Revision: https://phab.mercurial-scm.org/D2030

sshpeer: extract pipe cleanup logic to own function So it can be used outside of instantiated classes. This is needed to support pipe creation before __init__ is called. Differential Revision: https://phab.mercurial-scm.org/D2029