tests/test-fuzz-targets.t

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

#require clang-libfuzzer test-repo
  $ cd $TESTDIR/../contrib/fuzz
  $ make
Just run the fuzzer for five seconds to verify it works at all.
  $ ./bdiff -max_total_time 5